Frequent Xpra reconnects and freezes

[MoritzWeber0]

Since #332, we see frequent reconnects and session freezes, making the session effectively unusable.

The client tries to connect a few times and then disconnects:

Sometimes a valid connection is established, but it freezes after ~10 seconds and then tries to reconnect. Also when switching to another tab, it reconnects.

The backend Xpra log doesn't contain any useful information, but the console log is rather interesting and attached:
console.log

The backend version is xpra v6.2.1-r0.

[MoritzWeber0]

Corresponding issue with more details tracked in the Xpra HTML5 repository: Xpra-org/xpra-html5#328