Sometimes, loading doesn't stop -> improve internal error handling

[stefandesu]

Unfortunately, I couldn't find a way to reproduce this yet, but at the workshop yesterday we had multiple occasions where the loading doesn't stop. Once it happened on my machine, but only in Safari where I couldn't see the place in code where it happened, but it was some uncaught promise rejection.

A way to improve this would be to improve error handling to make sure that all promise rejections are caught properly and print helpful information on the console if possible.

[stefandesu]

Not sure if it will fix this particular error, but I added some error catching at various places where it could have failed. I'm closing this for now, we should open a separate issue when we are able to find a way to reproduce the bug.