Thanks @sdetweil. I did end up downloading the ICS and finding the event in Google Calendar. It was some sort of weird situation where there was an old event that had a repeating frequency and an end date that was before the event itself. How did that happen in the first place I don’t know!?
Anyway after modifying that event the whole thing is working again, so thank you and this one can go in the closed bin. Good to know how to troubleshoot this now.