stuck after killing the boss/ bugged unique mob

its the copper citadel there isnt a checkpoint in this area after killing the boss and i cant go back to the rest of the map to finish things i havent done yet wasting this t16 map i used.

also zotlec the high priest i bugged, when i was fighting it it dove into the ground and got stuck there and wwouldnt come back out so i could kill it.

https://imgur.com/a/99MQGaJ

also strong boxes bugged as well, just used alchemy on normal strong box and it wont activate.