EDIT: Workaround found. Had to continue playing past 50 and then intentionally die for it to pop.
MAY 30, 2017 POST
I frigin shredded my voice to get that far. All them deaths on the floor 40 boss... 7 HOURS to get to 50, and put down that zombified ballerina.
Then when I finally won, there was no achievement trigger at all! None after the kill, none after exiting, it NEVER HAPPENED! WTF
Where is my achievement??? :mad: