Trial didn't provide enough mobs for a boss

[Ender1970]

Just ran into something I've not seen mentioned here or encountered before. I am working on unlocking speedrunning gear. On trial level 3 I cleared the level of mobs (circled it 3 times to be sure), but I was at around 98% full on the temperature bar to trigger the boss. Is there anything that can be done at that point, besides leave and try again? At least I wasn't pushing in the ANB...

[Travis | Support Mgr.]

This happens on rare occasions. It used to happen commonly when Trials were first added.