I am playing single player mode in the Bunker Hill. I have cleared all the pillboxes, cleared the main bunker, destroyed the tank from the West, but I have not "moved on" to the next level...

When I check the map by pulling the left trigger, the top left corner of the screen says to clear pillboxes and destroy all enemies. I have searched the whole map for a straggler enemy and have been unsuccessful.

Any suggestions?