Trialmaster challenge completes after second boss

Completed first 10 waves run no problem, got a piece of key and put it into the door.

Running second time - challenge progressed to room 7/10 only (second boss). After killing the boss "Trial Complete" message appeared, instead of allowing to proceed further.

Treasure room unlocked, but no door to Trialmaster himself.
Tried a few time - every time the trial completes on room 7/10 and no access to Trialmaster.

Nevermind, apparently those were lower level keys to open the trial, which do not progress past 7.