All I can say is that hogs are known to sometimes wake up during hibernation and move and even build new nests. So it is possible that a hog awoke. I am assuming you don’t have cameras on the boxes in which case it needn’t have been a hog that triggered the straw indicators. A cat or even a rat could have disturbed them. But also, another hedgehog could have visited if, for instance, their usual food source had ceased. All sorts of perfectly feasible possibilities.
I wouldn’t worry about them disappearing too early. The adult males tend to disappear a fair bit earlier than the females, but then tend to return earlier too.
