Mob walled off in maps, unable to finish map. REF# 1,775,205,237

running a map in Savannah , T12 or something it was level 76. my bug ref # is 1,775,205,237. i could not complete the map. there was a rare spider mob with the minions stuck in a small circle area walled off in my map. could not aoe and could not use flame wall with fortress to go around the wall.