API web socket hangs?

I'm have set up ComfyUI (through Stability Matrix) on a Mac and using the code from web socket API usage example, every ~20 the processing hangs without any errors in ComfyUI console, there are always the same message sequence coming from the web socket before that happens:

{"type": "status", "data": {"status": {"exec_info": {"queue_remaining": 0}}, "sid": "2180aded-7cc9-4334-b5ba-b7c557449cb7"}}
{"type": "status", "data": {"status": {"exec_info": {"queue_remaining": 1}}}}
{"type": "status", "data": {"status": {"exec_info": {"queue_remaining": 1}}}}
{"type": "execution_start", "data": {"prompt_id": "29d86146-e600-4c3b-89b7-3c76bc09d8b5"}}

Any ideas what might be happening?