I am told no one raided the base and the dome was still present outside but it had a hole in the wall and it had 20 min left...

Inactive in 20 minutes is your status, not the event 

I don't know why 2 walls are missing. this has never happened before. whatever the cause, it is likely why your events do not despawn properly either. this very much sounds like a libgdiplus issue so I'm surprised your server is not hosted on a linux machine.