It would usually happen in go town battles compared to castle. Once they get stuck i would have to enable cheat mode on to wipe the last guys behind walls(happened three times to me now) Happened on a Aseria town, khuzait, and empire. Usually with big battles when defenders have more than 600 people on their side at the start of the match. Probably has to do with the sheer amount and them getting pushed in. From a crack due to it .