Boss unkillable in vaal temple

I ran a vaal temple, and got stuck in a generator room with a boss. I didn't see the boss but it ran underground with some burrowing visual effects, but never reappeared. My friend has had the same issue and think it was because the boss was stunned underground, and then never came up. it was also immune to damage while there, and room doors were locked. It could still be knocked around with spearfield knockback support.

lost ~90% of that temple, including a t3 offering room, with at the time the same value as my entire bank, pls fix, was my 3rd temple so i really dont feel like touching that mechanic rn... -.-

Also have a video of that boss being hit but with no damage taken.