Rare Monster stuck underground

Bug Report reference number: 2'742'294'331

One rare monster got stuck underground. It could not be attacked nor damaged by AOE. But it coult attack me, even though it was stuck at the same place and didn't move. Sad it was a rare cause it made me fail the map. Tried to go to Hero Selection and join the map again but it didn't help.

Had this happen with a unique monster spawn for a vaal beacon, report reference number is 4,239,965,397