Hi z64, sorry I just now got the email alert for the bug.
I didn't notice the console alert, sorry about that. I reproduced it here, at least I think so:
To be clear, I'm behind a corporate proxy, which sometimes has trouble with websockets. However, I think that you'll still want to get it working, as I can guarantee a portion of your user-base will also have to deal with proxies.
As an example, I also have trouble with AWS Cloudshell from behind our proxy.