PoE2: Immured <I_Forget>

I was fighting Immured Anger? (Special boss for cleansed nodes) on a fortress map and the boss teleported to the 'backdrop' ground. It was a place I couldn't get to.

I was lucky to be able to hit him and he eventually came back up. Before that, I tried porting to my hideout (no luck). I also moved pretty far away, no luck. I was trying to reset him.

Same. Fury boss on this map. Was to tag him with a ranged attack and deaw him up for a second, but then he went way out of range.