Both Fang lair and Falkreath hold have serious issues with despawning mobs and fight resets. The Senche fight in Fang Lair just likes to constantly reset( rather than start), and you have to use prox aggro for them to be 'interested' and not chain despawn. Falkreath Hold is far worse with Cernunnon and friends despawning at 50% and resetting the fight back to 100% . This makes doing a vFH run amazingly annoying and achieves almost impossible.
On Cernunnon we had close to 10 attempts to finish him, and finally gave up after each one resulted in him resetting to 100% after dying at 50%, instead of his 3 friends spawning and the fight continuing.
This is not limited to these zones, but these two seem especially problematic. I am also seeing strange despawns in vDSA and trials too.
This has been in several weeks now, but has never been addressed, nor have we had feedback about the bug.