I cannot delete calendar events and they become grey and white stripped

On iCal if I delete an event or decline it, occasionally it won't work and the event becomes partially greyed out with a white and grey stripe. No matter what I do, they just keep coming back. I have tried:

1. Delete them using iPhone, MacBook & PC - always return within a few minutes
2. Remove and re-add the calendar - always returns within a few days
3. Ask the person who made the event to delete/remove me - no effect
4. Change settings so only events 2 weeks old or less show - no effect

For context:

• I have 2x iPhones, MacBook, Windows 11 Pro PC - all are fully updated with latest OS
• If I remove the calendar from ALL devices, the issues always return
• The problem has been ongoing for years and nobody has ever been able to help

See image/example of how it looks today

• These are two different calendars, the video link is not always MS Teams or Google Meet