"ionic build --prod" throws several code errors that don't show up in regular builds

**Description:**
I have an Ionic app that is already almost done. Until now, I've been testing it with the regular `ionic build` method, and then using Capacitor to make an APK to test. That works well, just as the app does in the navigator, when developing it.

But when I try to use the `--prod` flag to optimize my code, I receive a huge amount of template errors that don't allow me to compile the code. Needless to say, these errors never show up on regular builds.

**Steps to Reproduce:**
Having a normally working version (both for Android and web), try to build a production version with `ionic build --prod`.

**Output:**
Here you have my output. You can see it mainly affects the templates:

```
> `

Error: src/app/app.component.html:10:5 - error NG8001: 'ion-menu' is not a known element:
1. If 'ion-menu' is an Angular component, then verify that it is part of this module.
2. If 'ion-menu' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message.

10
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

src/app/app.component.ts:18:16
18 templateUrl: 'app.component.html',
~~~~~~~~~~~~~~~~~~~~
Error occurs in the template of component AppComponent.

Error: src/app/app.component.html:10:60 - error NG8002: Can't bind to 'disabled' since it isn't a known property of 'ion-menu'.
1. If 'ion-menu' is an Angular component and it has 'disabled' input, then verify that it is part of this module.
2. If 'ion-menu' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message.
3. To allow any property add 'NO_ERRORS_SCHEMA' to the '@NgModule.schemas' of this component.

10
~~~~~~~~~~~~~~~~~~~~~~~~~

src/app/app.component.ts:18:16
18 templateUrl: 'app.component.html',
~~~~~~~~~~~~~~~~~~~~
Error occurs in the template of component AppComponent.

Error: src/app/app.component.html:10:86 - error NG8002: Can't bind to 'maxEdgeStart' since it isn't a known property of 'ion-menu'.
1. If 'ion-menu' is an Angular component and it has 'maxEdgeStart' input, then verify that it is part of this module.
2. If 'ion-menu' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message.
3. To allow any property add 'NO_ERRORS_SCHEMA' to the '@NgModule.schemas' of this component.

10
~~~~~~~~~~~~~~~~~~~

src/app/app.component.ts:18:16
18 templateUrl: 'app.component.html',
~~~~~~~~~~~~~~~~~~~~
Error occurs in the template of component AppComponent.

Error: src/app/app.component.html:11:7 - error NG8001: 'ion-header' is not a known element:
m1. If 'ion-header' is an Angular component, then verify that it is part of this module.
2. If 'ion-header' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message.

11
~~~~~~~~~~~~

src/app/app.component.ts:18:16
18 templateUrl: 'app.component.html',
~~~~~~~~~~~~~~~~~~~~
Error occurs in the template of component AppComponent.

Error: src/app/app.component.html:12:9 - error NG8001: 'ion-toolbar' is not a known element:
1. If 'ion-toolbar' is an Angular component, then verify that it is part of this module.
2. If 'ion-toolbar' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message.

12
~~~~~~~~~~~~~

src/app/app.component.ts:18:16
18 templateUrl: 'app.component.html',
~~~~~~~~~~~~~~~~~~~~
Error occurs in the template of component AppComponent.

Error: src/app/app.component.html:13:11 - error NG8001: 'ion-title' is not a known element:
1. If 'ion-title' is an Angular component, then verify that it is part of this module.
2. If 'ion-title' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message.

13 Dromous App
~~~~~~~~~~~

src/app/app.component.ts:18:16
18 templateUrl: 'app.component.html',
~~~~~~~~~~~~~~~~~~~~
Error occurs in the template of component AppComponent.

Error: src/app/app.component.html:16:7 - error NG8001: 'ion-content' is not a known element:
1. If 'ion-content' is an Angular component, then verify that it is part of this module.
2. If 'ion-content' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message.

16
~~~~~~~~~~~~~

src/app/app.component.ts:18:16
18 templateUrl: 'app.component.html',
~~~~~~~~~~~~~~~~~~~~
Error occurs in the template of component AppComponent.

Error: src/app/app.component.html:17:9 - error NG8001: 'ion-list' is not a known element:
1. If 'ion-list' is an Angular component, then verify that it is part of this module.
2. If 'ion-list' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message.

17
~~~~~~~~~~~~~~~~~~~~~~~~~~~

src/app/app.component.ts:18:16
18 templateUrl: 'app.component.html',
~~~~~~~~~~~~~~~~~~~~
Error occurs in the template of component AppComponent.

Error: src/app/app.component.html:18:11 - error NG8001: 'ion-item' is not a known element:
1. If 'ion-item' is an Angular component, then verify that it is part of this module.
2. If 'ion-item' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message.

18
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

src/app/app.component.ts:18:16
18 templateUrl: 'app.component.html',
96m ~~~~~~~~~~~~~~~~~~~~
Error occurs in the template of component AppComponent.

Error: src/app/app.component.html:18:48 - error NG8002: Can't bind to 'routerDirection' since it isn't a known property of 'ion-item'.
1. If 'ion-item' is an Angular component and it has 'routerDirection' input, then verify that it is part of this module.
2. If 'ion-item' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message.
3. To allow any property add 'NO_ERRORS_SCHEMA' to the '@NgModule.schemas' of this component.

18
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

src/app/app.component.ts:18:16
18 templateUrl: 'app.component.html',
~~~~~~~~~~~~~~~~~~~~
Error occurs in the template of component AppComponent.

Error: src/app/app.component.html:20:15 - error NG8001: 'ion-icon' is not a known element:
1. If 'ion-icon' is an Angular component, then verify that it is part of this module.
2. If 'ion-icon' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message.

20
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

src/app/app.component.ts:18:16
18 templateUrl: 'app.component.html',
~~~~~~~~~~~~~~~~~~~~
Error occurs in the template of component AppComponent.

Error: src/app/app.component.html:20:38 - error NG8002: Can't bind to 'name' since it isn't a known property of 'ion-icon'.
1. If 'ion-icon' is an Angular component and it has 'name' input, then verify that it is part of this module.
2. If 'ion-icon' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message.
3. To allow any property add 'NO_ERRORS_SCHEMA' to the '@NgModule.schemas' of this component.

20
~~~~~~~~~~~~~~~

src/app/app.component.ts:18:16
18 templateUrl: 'app.component.html',
~~~~~~~~~~~~~~~~~~~~
Error occurs in the template of component AppComponent.

Error: src/app/app.component.html:21:15 - error NG8001: 'ion-label' is not a known element:
1. If 'ion-label' is an Angular component, then verify that it is part of this module.
2. If 'ion-label' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message.

21
~~~~~~~~~~~

src/app/app.component.ts:18:16
18 templateUrl: 'app.component.html',
~~~~~~~~~~~~~~~~~~~~
Error occurs in the template of component AppComponent.

Error: src/app/app.component.html:26:9 - error NG8001: 'ion-list' is not a known element:
1. If 'ion-list' is an Angular component, then verify that it is part of this module.
2. If 'ion-list' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message.

26
m ~~~~~~~~~~~~~~~~~~~~~~~~~~

src/app/app.component.ts:18:16
18 templateUrl: 'app.component.html',
~~~~~~~~~~~~~~~~~~~~
Error occurs in the template of component AppComponent.

Error: src/app/app.component.html:27:11 - error NG8001: 'ion-menu-toggle' is not a known element:
1. If 'ion-menu-toggle' is an Angular component, then verify that it is part of this module.
2. If 'ion-menu-toggle' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message.

27
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

src/app/app.component.ts:18:16
18 templateUrl: 'app.component.html',
~~~~~~~~~~~~~~~~~~~~
Error occurs in the template of component AppComponent.

Error: src/app/app.component.html:28:13 - error NG8001: 'ion-row' is not a known element:
1. If 'ion-row' is an Angular component, then verify that it is part of this module.
2. If 'ion-row' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message.

m28
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

src/app/app.component.ts:18:16
18 templateUrl: 'app.component.html',
~~~~~~~~~~~~~~~~~~~~
Error occurs in the template of component AppComponent.

Error: src/app/app.component.html:28:43 - error NG8002: Can't bind to 'routerDirection' since it isn't a known property of 'ion-row'.
1. If 'ion-row' is an Angular component and it has 'routerDirection' input, then verify that it is part of this module.
2. If 'ion-row' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message.
3. To allow any property add 'NO_ERRORS_SCHEMA' to the '@NgModule.schemas' of this component.

28
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

src/app/app.component.ts:18:16
18 templateUrl: 'app.component.html',
~~~~~~~~~~~~~~~~~~~~
Error occurs in the template of component AppComponent.

Error: src/app/app.component.html:30:15 - error NG8001: 'ion-col' is not a known element:
1. If 'ion-col' is an Angular component, then verify that it is part of this module.
2. If 'ion-col' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message.

30
~~~~~~~~~~~~~~~~~~

src/app/app.component.ts:18:16
18 templateUrl: 'app.component.html',
~~~~~~~~~~~~~~~~~~~~
Error occurs in the template of component AppComponent.

Error: src/app/app.component.html:37:15 - error NG8001: 'ion-col' is not a known element:
1. If 'ion-col' is an Angular component, then verify that it is part of this module.
2. If 'ion-col' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message.

37
~~~~~~~~~

src/app/app.component.ts:18:16
18 templateUrl: 'app.component.html',
~~~~~~~~~~~~~~~~~~~~
Error occurs in the template of component AppComponent.

Error: src/app/app.component.html:50:13 - error NG8001: 'ion-item' is not a known element:
1. If 'ion-item' is an Angular component, then verify that it is part of this module.
2. If 'ion-item' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message.

50
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

src/app/app.component.ts:18:16
18 templateUrl: 'app.component.html',
~~~~~~~~~~~~~~~~~~~~
Error occurs in the template of component AppComponent.

Error: src/app/app.component.html:50:50 - error NG8002: Can't bind to 'routerDirection' since it isn't a known property of 'ion-item'.
1. If 'ion-item' is an Angular component and it has 'routerDirection' input, then verify that it is part of this module.
2. If 'ion-item' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message.
3. To allow any property add 'NO_ERRORS_SCHEMA' to the '@NgModule.schemas' of this component.

50
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

src/app/app.component.ts:18:16
18 templateUrl: 'app.component.html',
~~~~~~~~~~~~~~~~~~~~
Error occurs in the template of component AppComponent.

0mError: src/app/app.component.html:52:15 - error NG8001: 'ion-icon' is not a known element:
1. If 'ion-icon' is an Angular component, then verify that it is part of this module.
2. If 'ion-icon' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message.

52
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

src/app/app.component.ts:18:16
18 templateUrl: 'app.component.html',
~~~~~~~~~~~~~~~~~~~~
Error occurs in the template of component AppComponent.

Error: src/app/app.component.html:52:38 - error NG8002: Can't bind to 'name' since it isn't a known property of 'ion-icon'.
1. If 'ion-icon' is an Angular component and it has 'name' input, then verify that it is part of this module.
2. If 'ion-icon' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message.
3. To allow any property add 'NO_ERRORS_SCHEMA' to the '@NgModule.schemas' of this component.

52
~~~~~~~~~~~~~~~

m src/app/app.component.ts:18:16
18 templateUrl: 'app.component.html',
~~~~~~~~~~~~~~~~~~~~
Error occurs in the template of component AppComponent.

Error: src/app/app.component.html:53:15 - error NG8001: 'ion-label' is not a known element:
1. If 'ion-label' is an Angular component, then verify that it is part of this module.
2. If 'ion-label' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message.

53
~~~~~~~~~~~

src/app/app.component.ts:18:16
18 templateUrl: 'app.component.html',
~~~~~~~~~~~~~~~~~~~~
Error occurs in the template of component AppComponent.

Error: src/app/app.component.html:59:13 - error NG8001: 'ion-item' is not a known element:
1. If 'ion-item' is an Angular component, then verify that it is part of this module.
2. If 'ion-item' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message.

59
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

src/app/app.component.ts:18:16
18 templateUrl: 'app.component.html',
~~~~~~~~~~~~~~~~~~~~
Error occurs in the template of component AppComponent.

Error: src/app/app.component.html:60:15 - error NG8001: 'ion-icon' is not a known element:
1. If 'ion-icon' is an Angular component, then verify that it is part of this module.
2. If 'ion-icon' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message.

60
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

src/app/app.component.ts:18:16
18 templateUrl: 'app.component.html',
~~~~~~~~~~~~~~~~~~~~
Error occurs in the template of component AppComponent.

Error: src/app/app.component.html:60:38 - error NG8002: Can't bind to 'name' since it isn't a known property of 'ion-icon'.
1. If 'ion-icon' is an Angular component and it has 'name' input, then verify that it is part of this module.
2. If 'ion-icon' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message.
3. To allow any property add 'NO_ERRORS_SCHEMA' to the '@NgModule.schemas' of this component.

60
~~~~~~~~~~~~~~~~~~~~~

src/app/app.component.ts:18:16
18 templateUrl: 'app.component.html',
~~~~~~~~~~~~~~~~~~~~
Error occurs in the template of component AppComponent.

Error: src/app/app.component.html:61:15 - error NG8001: 'ion-label' is not a known element:
1. If 'ion-label' is an Angular component, then verify that it is part of this module.
2. If 'ion-label' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message.

61
~~~~~~~~~~~

src/app/app.component.ts:18:16
18 templateUrl: 'app.component.html',
~~~~~~~~~~~~~~~~~~~~
Error occurs in the template of component AppComponent.

Error: src/app/app.component.html:69:5 - error NG8001: 'ion-router-outlet' is not a known element:
1. If 'ion-router-outlet' is an Angular component, then verify that it is part of this module.
2. If 'ion-router-outlet' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message.

69
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

src/app/app.component.ts:18:16
18 templateUrl: 'app.component.html',
~~~~~~~~~~~~~~~~~~~~
Error occurs in the template of component AppComponent.

Error: src/app/app.component.html:8:1 - error NG8001: 'ion-app' is not a known element:
1. If 'ion-app' is an Angular component, then verify that it is part of this module.
2. If 'ion-app' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message.

8
~~~~~~~~~~~~~~~~~~~~~~~~~~~

src/app/app.component.ts:18:16
18 templateUrl: 'app.component.html',
~~~~~~~~~~~~~~~~~~~~
Error occurs in the template of component AppComponent.

Error: src/app/app.component.html:9:3 - error NG8001: 'ion-split-pane' is not a known element:
1. If 'ion-split-pane' is an Angular component, then verify that it is part of this module.
2. If 'ion-split-pane' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message.

9
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

src/app/app.component.ts:18:16
18 templateUrl: 'app.component.html',
~~~~~~~~~~~~~~~~~~~~
Error occurs in the template of component AppComponent.

Error: src/app/event-creation/event-creation.component.html:161:26 - error TS2339: Property 'promptResetPoly' does not exist on type 'EventCreationComponent'.

161
~~~~~~~~~~~~~~~

src/app/event-creation/event-creation.component.ts:21:16
21 templateUrl: './event-creation.component.html',
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Error occurs in the template of component EventCreationComponent.

Error: src/app/forgotten-pw/forgotten-pw.component.html:13:10 - error TS2339: Property 'response' does not exist on type 'ForgottenPwComponent'.

13 {{ response }}
~~~~~~~~

src/app/forgotten-pw/forgotten-pw.component.ts:7:16
7 templateUrl: './forgotten-pw.component.html',
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Error occurs in the template of component ForgottenPwComponent.

Error: src/components/entities-list/entities-list.component.html:16:54 - error TS2345: Argument of type 'number' is not assignable to parameter of type 'string'.

16 {{ mapEntity?.get("description") | limitTo : 180 }}
~~~

src/components/entities-list/entities-list.component.ts:7:16
7 templateUrl: './entities-list.component.html',
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Error occurs in the template of component EntitiesListComponent.

Error: src/components/entities-list/entities-list.component.html:4:47 - error TS2341: Property 'iconGetter' is private and only accessible within class 'EntitiesListComponent'.

4
~~~~~~~~~~

src/components/entities-list/entities-list.component.ts:7:16
7 templateUrl: './entities-list.component.html',
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Error occurs in the template of component EntitiesListComponent.

Error: src/components/training-control/training-control.component.html:12:50 - error TS2339: Property 'start' does not exist on type 'Training'.

12

~~~~~

src/components/training-control/training-control.component.ts:10:16
10 templateUrl: './training-control.component.html',
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Error occurs in the template of component TrainingControlComponent.

Error: src/components/training-control/training-control.component.html:56:74 - error TS2339: Property 'step' does not exist on type 'TrainingControlComponent'.

56 Volver
~~~~

msrc/components/training-control/training-control.component.ts:10:16
10 templateUrl: './training-control.component.html',
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Error occurs in the template of component TrainingControlComponent.

[ERROR] An error occurred while running subprocess ng.

ng.cmd run app:build:production exited with exit code 1.
`
```

**My `ionic info`:**

`Ionic:

Ionic CLI : 6.11.1 (C:\Users\zerok\AppData\Roaming\npm\node_modules\@ionic\cli)
Ionic Framework : @ionic/angular 5.5.4
@angular-devkit/build-angular : 0.1101.4
@angular-devkit/schematics : 9.1.9
@angular/cli : 11.1.4
@ionic/angular-toolkit : 2.2.0

Capacitor:

Capacitor CLI : 2.4.6
@capacitor/core : 2.4.6

Utility:

cordova-res : not installed
native-run : not installed

System:

NodeJS : v15.7.0 (C:\Program Files\nodejs\node.exe)
npm : 6.14.11
OS : Windows 10`

Reproduce the reported failure with `ionic build --prod` using an otherwise working Ionic app, then inspect the Ionic CLI production-build entry point and its Angular build configuration. Compare the production and regular build output, and consider the issue done when the production build completes without the reported unknown Ionic element and property template errors.

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