Rare monster out of map limits

Happened one time in tier 10 map. I did clear the whole map, but a yellow skull indicates one rare monster left.. the skull was out of map. Did try every corner of the map but could not found a way to find the monster.

I also find it bad design that you need to kill all rares. Atleast make some checkpoint teleportation system like in campaign. It is very frustrating to travel all the way back to beginning in a large map if you missed one monster in the start.

Playing tier4 map right now. one skull left but it is behind an impassable wall in an oasis map. I can not finish the map.

https://www.imghippo.com/i/IWL3030mys.png