Invunerable bugged mosnter in temple - stuck in room ahd to quit out

Bug: invunerable(bugged) monster is in room, cannot exit out the room

So the setup is the following:

-Enter temple with 3/12 (crystals?) (didnt even know i could do that) (maybe doesnt matter)
-Go into dynamo room
-Rare sun priest is inside
-chunk it to half HP
-He goes underground/invisible??????????????
-untargetable by skills, can still mark him with snipers mark but he is invisible/damage immune
-I think he still does damage
-literally stuck in the room with him
-quit out the temple is the only solution