ionic serve yielding unstable server

# Bug Report

**Ionic Info**
Run `ionic info` from a terminal/cmd prompt and paste the output below.

```
$ ionic info
√ Gathering environment info - done!

Ionic:

ionic (Ionic CLI) : 4.1.1
Ionic Framework : @ionic/angular 4.0.0-beta.5
@angular-devkit/core : 0.7.5
@angular-devkit/schematics : 0.7.5
@angular/cli : 6.1.5
@ionic/ng-toolkit : 1.0.7
@ionic/schematics-angular : 1.0.5

System:

NodeJS : v8.9.0 (C:\Program Files\nodejs\node.exe)
npm : 6.1.0
OS : Windows 8.1
```

**Describe the Bug**
When I serve any ionic project, including starters, everthing seems to work fine (no errors reported), but the page load fails in the browser (both chrome and firefox). I get "Loading..." on the tab while the source is compiling, but when it is done the page is blank.

If I refresh the page continually (or wait a few minutes and then refresh), it will eventually load.

I have the same problem every time I make any change to the code - I have to wait a few minutes before it will load correctly.

**Steps to Reproduce**
Steps to reproduce the behavior:
1. Clone blank starter
2. `ionic serve`

**Expected Behavior**
It should just work like it used to in the past.

**Additional Context**
I sometimes get the following error in the console:
`Failed to load resource: net::ERR_ADDRESS_IN_USE`

If I check the network tab in chrome, I see that some files are failing to load. The failing files change if I continually refresh, but are always some combination of the following files:
styles.js
vendor.js
polyfill.js
main.js

Start by running `ionic serve` on the blank starter under the reported Windows and Node.js setup, then inspect the browser console and network tab for the changing failures in `styles.js`, `vendor.js`, `polyfill.js`, and `main.js`. Reproduce the blank page after a source change and confirm that the served page loads reliably without `ERR_ADDRESS_IN_USE`.

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