Citadel left with one monster.. Cant complete map

The last 2 times a ran a Citadel on the Ezomyte City biome it has left me with one monster and i cant finish map. Ive run through the maps for 20 min after clearing it never to find last enemy. Not being able to complete the map blocks path on map device.

Had that happen on Copper Citadel last night...1 guy stuck in the floor spamming fire circles but no way to kill him. Got my frags but said map failed. In fact all citadels on my map show red even though they were cleared except for last nights 1.