Calendar

Just got a new iPhone XS Max, and my work calendar keeps populating and then disappearing over and over. It’s very frustrating and inconvenient. I have tried restarting the phone. When it’s gone, I go into the “calendars “ tab at the bottom of the calendar app and the work calendar is checked but then it’s like my phone is like, oh right, the work calendar. And then it checks off like 5 work calendar entries. But then a few hours later, it’s gone again. Help!