It was clean, which removes all of the usual suspects for reboots. Basically, it implies that you initiated the reboot somehow
BTW, you've got some plugin issues:
preclear.disk.plg - 2021.04.11 (Up to date) (Incompatible)
statistics.sender.plg - 2017.09.22 (Up to date) (Incompatible)
These should be removed and replaced with Unassigned Devices Preclear
Unraid-Kernel-Helper.plg - 2021.03.17 (Unknown to Community Applications)
This should be removed completely.