I fixed mine in game this week but I'm waiting for the update to seal the deal.
I had to move all my sims out of the city and relocate them in other worlds with family members (8 households).
I then deleted any non-played sims from the world to make sure no remnants of the corrupt festival where in the city.
I then deleted all the festival objects in the 8 households that lived in my city after relocating them.
I then restarted my save as a new game and made duplicates and tested the San Myshuno's festivals.
Everything is working smoothly right now. The festivals are coming and disappearing like they should.
My San Myshuno is the same as it always has been for me. All my apartments are furnished and still intact waiting for their owners to move back.
Squatters are probably going to move in while my sims are relocated...I'll delete them when the city is safe for my sims again.