Communication with the websocket in the docker is falling, why?

Question

Docker

Good afternoon! There is a docker that works with a websocket, I receive data via a websocket from an external service, periodically pinging with response messages so that the websocket does not close. Everything works fine on the local machine, having placed the prod on the server, the websocket connection is constantly falling and I cannot write messages (ping). I do not understand what could be the reason, with an equal environment. Unless the characteristics are different, but there is no load, and everything as a whole works smartly. The Internet channel on the server itself is also not bad. What could be the matter, and how can this story be debugged at all?