You probably have a silver-haired or hoary bat. Both species migrate south in winter. But several other Oregon bats don’t migrate. Although it’s unlikely that a bat box would be used as a winter hibernaculum, I would still leave it up in winter. There’s no reason to take it down except to make it last longer.

I wouldn’t clean the box unless you start finding dead bats on the ground below. Bat feces typically falls to the ground and doesn’t pose a sanitation issue for the bats in the box. Further, depending on what you cleaned it with, you might find that bats will not use the box because they have an acute sense of smell.