Deleted reminders won’t leave calendar

I have a Reminders list shared with my partner for joint tasks. We both have iPhone 12 Pro Max’s and when we updated to iOS 18.0 the reminders showed up in the Calendar app like all the other ones, no issues there. But then there were some reminders that they didn’t want to have on the shared list anymore, so I moved those reminders from the shared list to a new list that only I had.

The reminders are still visible in their Calendar app. When clicked on in the Calendar app any options to edit, view, or delete the reminder will launch the Reminders app on whatever page it’s on, but the deleted reminders aren’t visible in the Reminders app.

If you try “check off” the reminder in Calendar where it’s visible it just unchecks itself a second later, and it seems to be marked as repeating daily even though it never originally should have been.

To try fix this I then moved the reminders back from the new private list to the original shared list to try edit it from my partner’s phone that was having this issue. But this just brought them across while keeping the faulty reminders still in the Calendar app. So then I use their phone to delete the reminders, and they disappear, but the duplicate “repeat daily” ones don’t leave. So then I delete all completed reminders and go to the Deleted Reminders list to permanently delete them, and then delete the whole shared reminders list to be safe. But the faulty ones still show up in Calendar.

I’ve also tried restarting both iPhones, unchecking the “show reminders in calendar” and checking it again, force quitting both apps, all the basics. But it’s still there, and there’s quite a few of them, and they’re clogging up multiple days’ worth of calendar events. I’d rather not have to just have Calendar not show reminders anymore and lose that iOS 18 feature, so any other suggestions I can try would be appreciated.