Possible memory leak

I have two game servers running with an Undertow websocket server, and I notice on both games that over time, WebSocket13Channel objects start filling all the memory.

I did a heap dump after 24 hours of running one of the servers (with only 34 players online at that moment), and this was the result:

(see Screenshot_7.png)

The only related thing I see in the logs are this kind of error:

(See the other screenshots)