Fortress map cannot be completed. 3 monsters remain.

Ran through the whole map three times now and I cannot find any remaining monsters. It's got those burrowing shellfish so not sure if it's one of those, but the game does not point me to the last rare at all so not sure what's going on. Anyway the map cannot be finished. I think it is irradiated with 14% more rare mobs and rare mobs have a 50% chance for 1 more modifier.