Is it at set times when you charge? Just wondering if you have the Auto Restart at set times option turned on. You can check this by going into settings. Then battery and device care. Tap on the 3 dots at the top right. Go into Automation Second option down is the setting
I've found a lot in there as you say, and none of it I knew about! I've optimised whilst there too... so I think a hour tonight having a nosey will make "a bit" of difference!