I will change the title of the report, this is different from the bug we fixed. 
When we changed the spawn code to be more performant, it meant that it would always find a location to spawn enemies, but that location didn’t need to be reachable.
For hearthlings, we tried to make them spawn close/around the banner if the scenario from that bug happened (choosing the spot where the banner is as the spawn location), but apparently it can still include unreachable locations.