Shortly after startup (within 60 seconds) when all the tasks are executing, sonarr just locks up. It appears that all threads are frozen (the http service isn’t responsive, no background tasks execute, etc.). There is no CPU usage, there is no disk activity or network activity. There are no logs after sonarr appears to freeze (in trace mode).
So after several hours of debugging sonarr, then the mono runtime (the whole runtime was frozen too), it turns out the problem was a conflict between the Docker overlay storage driver and CephFS. I believe mono would hang shortly a certain file was accessed.