shim is required Error

Hey out there,

we are totally stuck by a recently occuring error.

We use reflect-metadata 0.1.10 in our angular-starter project. We also use Angular 4.2.5 and Typescript 4.2.1

We switched our whole building system days ago and can not figure out, why this error occurs.

Uncaught reflect-metadata shim is required when using class decorators
DecoratorFactory @ main.5882b9f….bundle.js:1
(anonymous) @ main.5882b9f….bundle.js:1
YWx4 @ main.5882b9f….bundle.js:1
__webpack_require__ @ main.5882b9f….bundle.js:1
Iksp @ main.5882b9f….bundle.js:1
__webpack_require__ @ main.5882b9f….bundle.js:1
7G6f @ main.5882b9f….bundle.js:1
__webpack_require__ @ main.5882b9f….bundle.js:1
fYOR @ main.5882b9f….bundle.js:1
__webpack_require__ @ main.5882b9f….bundle.js:1
+1L/ @ main.5882b9f….bundle.js:1
(anonymous) @ main.5882b9f….bundle.js:1

Our polyfills file looks good, I guess:

import 'core-js/es6/array';
import 'core-js/es6/date';
import 'core-js/es6/function';
import 'core-js/es6/map';
import 'core-js/es6/math';
import 'core-js/es6/number';
import 'core-js/es6/object';
import 'core-js/es6/parse-float';
import 'core-js/es6/parse-int';
import 'core-js/es6/reflect';
import 'core-js/es6/regexp';
import 'core-js/es6/set';
import 'core-js/es6/string';
import 'core-js/es6/symbol';
import 'core-js/es6/typed';
import 'core-js/es6/weak-map';
import 'core-js/es6/weak-set';
import 'core-js/es7/reflect';
import 'reflect-metadata';
import 'zone.js/dist/zone';
if ('production' !== ENV) {
    Error.stackTraceLimit = Infinity;
    require('zone.js/dist/long-stack-trace-zone');
}

The error occurs, when we act as a "normal" user and UNCHECK "disable cache" in our devTools. When we switch routes the error occurs. When we CHECK "disable cache" there seems to be no problem.

Any guesses? We appreciate your help. Thanks

Start with the shown polyfills file and reproduce the route switch with browser cache enabled and disabled. Trace why the reflect-metadata shim is unavailable in one case; done means identifying the cause and documenting a verified resolution or reproduction.