Calendar Refresh

A couple of our users have access to another user’s calendar. They are responsible for creating appointments on that person’s calendar. The calendar normally would refresh on its own after an update so that users were not overbooking on that calendar. About 3 weeks ago, this auto-refresh stopped occurring. I have not found any setting that would change this. It’s probably real simple and I’m just not seeing it but any help would be awesome. TIA