ember-cli: `ember test --server` stops building and refreshing the browser after a while

Intro

We have been noticing the same behavior across all our apps at work and I was able to reproduce on a brand new app

The issue

After an amount of time that “seems” to be hovering around 20-30 minutes ember test --server stops sending the “start test” message over the websocket when files are changed. Even opening a new tab or a new window in a different browser does not fix the issue. All connected clients will not be notified when the code is changed.

Furthermore (although I have less proof of this) even though ember test --server seems to recompile when code is changed it looks like the assets being server are not different and changes don’t make their way into the compiled assets

The only fix is to restart ember test --server

reproduction

ember new test-app
cd test-app
yarn
ember test --server
# open browser and visit test page, 
# make a change to app/app.js
# see page reload
# wait 20 min or so
# make a change to app/app.js
# page won't reload
# change is not reflected in new source code

thanks for listening, happy to provide any more context or take suggestions on how to move this forward!

---

Output from ember version --verbose && npm --version && yarn --version:

➜ ember --version
ember-cli: 3.21.0
node: 10.22.0
os: linux x64

➜ npm --version
6.14.6

➜ yarn --version
1.22.5

note that I was able to reproduce this on node 12 as well