Only default calendar is checked
Sometimes when I load my calendar view, it switches to having only the default calendar checked. I have four other calendars linked/imported, and it's annoying to have to check them again every time.
Rukumouru Hakure commented
I have this issue as well. Calendar visibility should be saved across sessions. If I hide a calendar, have it hidden next time I open Outlook. If I unhide it, have it visible next time!