I kept wondering why Jenkins wanted to shut down when I got to work in the morning, and I finally spotted this in the logs:
So I changed the ThinBackup settings and removed the checkbox concerning waiting/forcing idle. It saved the settings, but didn't seem to tell the running process/thread, because after canceling the "shutdown" from the GUI, it immediately tried again with the same log message.
Expected outcome: After telling it NOT to try to force an idle state, it should have stopped trying.
(Also, there's a typo in that INFO message.)