Small client code change breaks whole app. Restart does not help

So since a recent version change I am getting very weird errors in Chrome, which completely break my app.
One second it works perfectly, all good, and after a very small code change sometimes this occurs:

I tried a simple npm install, I tried server node/meteor restarts. No change whatsoever, my app stays broken.

Meteor version:

I then have to run npm install @babel/runtime@7.0.0-beta.55 again to get my app to work again.
All very strange. I did not change anything regarding my packages in between.