The bots were stuck in a shutdown deadlock. A system exit call triggers the shutdown hook, and if that also invokes system exit then the system deadlocks. This could be triggered through the "admin shutdown" of a running game.
This update would fix the situation:
https://github.com/triplea-game/triplea/pull/15017
That update should roll out to bots in between games (there's an automatic restart between games, the bots have pulled the latest code version, they'll activate the new version on the next game restart)