Submitted Bug Report in game, but providing additional info here. Not sure how much is useful, but here’s the series of events:
Running Kriegval’s Rest with a one other party member. Stop in the second chamber to loot the Sturdy Chest. Jumped on top of the books on the left-hand side of the platform, but couldn’t fit under the ceiling. Resorted to jumping under the chest, and trying to get the click timing right. Experienced partial success: the chest “opened” but I did not receive any loot. There were two chest objects: the open, now-unlootable chest, and another lootable chest that I could just barely detect from the mouse cursor changing over certain areas.
After referring to the strategies of other players on Wowhead, I used the Mage’s Chewed Wand to polymorph myself and fit through the gap on the upper platform to get the rest of the loot.
On returning to my party member and entering combat, I experienced an almost complete freeze of maybe one frame every 3-4 seconds. The game only unlocked when my character had died. I resurrected and spawned at the entrance. At the bottom of the stairs, there were 3 Enchanted Candles. I picked one and ran through the map to where I had died.
Somewhere in the middle, the candle dropped. I’m not sure if I took damage from a fire turret or if it was something else. I could pick it up again no problem and moved on.
On catching up and entering combat again, I experienced the same freeze. I could hear some combat noises from which I could tell I was getting stacks of Smothering Shadows, despite still holding an Enchanted Candle with plenty of stacks of wax. My party member confirmed that I was taking on the debuff despite being within two AOEs of light, one from the candle I was holding and one from a candle they were holding.
After 15-20 seconds, the game crashed to desktop. My party member reported that the debuff on my character went away after I disconnected.
I’ve been able to log back in and not experienced any problems since.
EDIT: Additional context: my character is alliance and my party member is horde.
Also, for a period of time (until he died and resurrected) Brann was attackable.
And then, despite being a Bountiful Delve, no Bountiful chest spawned for me in the treasure room, though it did spawn for my party member.