Calendar Response Can't Be Sent
At some point I replied to a calendar event when I was offline. For about a month now I keep getting a pop up that my "Calendar Invitation: Your response to the invitation cannot be sent." It probably appears 10 or 12 times throughout the day and when I pick up my phone in the morning there are 7 or 8 of them that pop up at once and I have to respond to each of them before it will let me do anything.
How do I get these notifications to stop? I don't which event it was so I can't go back and change or resubmit my response or delete the event.
I've upgrade the iOS, force restarted the calendar app, restarted the phone. Nothing works.
Please help! This is maddening.
iPhone X, iOS 12