Inconsistent Thread Usage in Tyrus WebSocket Client During Initial Request Handling

Context: I have two annotated @OnMessage. One handles incoming binary, and the other is String.

I observed that the Tyrus WebSocket Client appears to use two threads (Grizzly(1) and Grizzly(2)) to handle the incoming data (binary and string) when I first run the program. The next time I re-run, it only uses one thread which is : Grizzly(1). Can anyone explain to me regarding this inconsistent thread usage on the client side? thankyou.