[Solved] Websocket error after upgrade to 7.8.9


I upgraded our test environment from 7.8.5 to 7.8.9 and now we get websocket error.
Can’t find any errors in our reverse proxy log.
Errors in the browser: Error during WebSocket handshake. WSClient websocket onerror. data: “isTrusted”:true
WSClient has been closed, connect fail count: 9
Polling websockets connection for stat: undefined (focalboard…)

How to find the issue here?

Best regards,

Okey found the solution here