[kaba0]

I’m fairly sure that’s just the idiot “shutdown is replaced by hibernate” of Windows doing something hard to explain. In short, if you press on the shutdown option in Windows it will instead hibernate by default to make “boots” faster. You have to shift-+click on the poweroff option on the menu for the behavior you want.

What probably happens is that it assumes it is the only OS and goes into another mode if not used for a few days? (This part I’m not sure about but the previous paragraph is true). But perhaps Ubuntu is your default in the boot order? Nonetheless, try to poweroff your windows with this shift+click and check if that solves the problem.