Calendar Sharing has Stopping Updating

My husband and I got new iphones. Mine is a 17Pro, his a 16E. We share our iphone calendars. It was working fine since October and suddenly stopping updating. He is able to see my calendar and updates on his phone. I am no longer seeing NEW items on his calendar. We are not aware of any changes we've made to the phones. We tried deleting my access to his calendar and re-adding it, but that is not showing new appointments either. Can anyone tell me how to fix this?