websocket not able to connect with no error reason [closed]

I have a web application which opens websocket to get some data, today (with no changes on server side) strange thing start happening. At application start (angular web page) websocket (rxjs) is not able to connect, and has no error message:
error message

And it’s more strange that after some time (usually 10-20 minutes) application finally able to connect to the web socket (it has reconnect logic in case if no data has been got):
retries

Any advises how to debug such situation?

I have a server on one of public cloud platfor (nginx as server with static pages + springboot), I did fresh deployment in different region and behavior is same no maters how many users are connected. I tried oldest images to be sure that nothing has changed in the code, but same result

Also no errors on springboot side