It seems to be failure of the libevent function event_base_dispatch(), which also logs `[warn] kevent: Bad file descriptor`:
``` 6(38960) DEBUG: http_async_client [hm_hash.c:59]: init_http_m_table(): hash table 0x10f7f82a8 initialized with size 2048 [warn] kevent: Bad file descriptor 6(38960) ERROR: http_async_client [async_http.c:97]: async_http_run_worker(): event base dispatch failed - ret: -1 (errno: 9 - Bad file descriptor) ```
The above logs are from current master, as I pushed a commit to http_async_client module to exit the worker process (and thus shutdown kamailio) in the case of this failure.
Could be something that changed in the new MacOS 12 kqueue implementation. I am not familiar with libevent, maybe @grumvalski or someone else can comment or analyse further.