Tier 3 key: This issue has happened twice in 4 runs now, I thought it might have happened from instantly killing all the bosses but the second time I killed them one by one with a few seconds between and has still happened, feels bad to lose a key and get no loot.
The only way is to logout. For what it is worth playing companion druid if it matters.
Same now on Tier 2 Barb. No loot 
Just had it happen to me as well on a T2 compass.
Had it happen twice on my WW barb, lowest tier key available. Worked fine yesterday?
M2 T3 compass, rogue.
Tier 1 key, rogue, beat all six waves, beat all bosses one by one and no loot, no mats and stuck in an empty council room. 
Boooooooo
Same here. Only thing of note is after killing last boss the fiery exploding enemies spawned as he was dying. Not sure if the adds are causing the issue.
Just happened to me again, tier 4.
Please note that from multiple sources (Personally experienced, Friends experience & someone in this post lol) that killing all the bosses before killing the EXPLODING MINION guys will cause this bug, so make sure to kill everything with a health bar before killing the final boss. This is the only way i know of that causes this bug, there may be more. Please share any other way to trigger this bug. Many thanks
still no fix after all this time? gg blizzard, showing your legendary ignorance or carelessness throughout all these years as always, a WHOLE season without fixing something that’s quite gamebreaking when we know that the whole point of diablo is to get better loot, and the main season content giving better loot doesn’t give any loot at all because of a bug ! nice !
This has happened to me three times this week and it’s not nearly the first time I’ve had the issue. Had the issue last season, and having it now. Come on Blizzard. Fix your issues that have been reported over and over again!
This is still a problem. After it happened to me in The Pit after a 10 minute run, then it happens in an Infernal Horde run. Will this ever be fixed? Losing the will to play.
Still broken in December. I’m going to try Path of Exile and see if it has less crashes and bugs.