Trial of Chaos Chimera boss room bugged, bricking run

Bug report reference number: 3,478,086,575.

I killed the chimera boss in room 4/10 but the door to the next challenge area is not opening.

The quest state is stuck showing "Enter the Challenge Area".

I wonder if this is because I blinked down to the bottom of the arena before the Trialmaster appeared.

I ran back up stairs towards the entrance, and then the Trialmaster appeared, but going back into the arena does not resolve the problem, and my run is now stuck.

An additional factoid in case it's relevant: I killed the Chimera quite quickly, and it died while it was flying in the air (breathing fire down to the ground) from poison.