Random items are disappearing from my calendar

I have an iPhone 14 up-to-date with it software and thought I was losing my mind and forgetting to put things in my calendar only to realize I’m putting them in the calendar and they are coming off. This has happened multiple times in the last 6 to 8 weeks. I also have an older iPad, which is usually syncing with my iPhone and I have a new iPad. The calendar entries are coming off of everything. I need to find out what’s going on. I am missing important dates and over lapping schedules.

i’ve checked all the settings and everything is set to all events to back up indefinitely

it also seems to affect items that I manually put in versus invites that come through someplace like Open Table or an airline.