Enabling domain proxy, timesout websockets

Hello, I’m self-hosting a instance of VaultWarden ( fork of BitWarden ), but noticed when I try to login to it with my phone nothing happens. Looking at the network tab in dev. tools of the browser I can see that the webpage connects to a websocket just fine, but after 30 seconds it throws out an error and timesout. Tried turning domain proxy off to see if it’s VaultWarden fault, but it works just fine then, no timeout and logins just fine.

Errors in networks tab:
Error: Server timeout elapsed without receiving a message from the server.
Unhandled Promise rejection: Server timeout elapsed without receiving a message from the server. ; Zone: <root> ; Task: null ; Value: Error: Server timeout elapsed without receiving a message from the server.
Error: Server timeout elapsed without receiving a message from the server.

Any recommendation what to do?