OneFuriousDon

Should have checked if Beni ZIlal owned any location (most likely Aserais). It happened to me several times when BZ used influence to force its enemy - Aserai - to give a location Aserai conquered to it's enemy BZ. (LOL) The crash happens when AI army tries to re-siege location it should have owned in the first place. I fixed it by concole-killing off Beni Zilal clan before AI managed to lay a siege.

Check if there are any Beni Zilal owned castles or towns.

There can be multiple reasons why it happens. I found, however, one persistent which happened to me multiple times until I figured it out and solved it via console. If this is the one you have - following should work for you as well: Load your save and check if there is any castle or town owned by a minor faction - most likely Beni Zilal in Aserai territory. If yes than this is the case. Open console and kill off every Beni Zilal clan member destroying it in the process. Corrupted location will turn to whomever should own it (99,99999% Aserai) because it should have been Aserai taking it in the first place but Beni Zilal - while at war with Aserai - used influence to force Aserai to give it to them (WTF?). This happened to me several times - twice I was the part of AI Aserai army taking the town and then trying to siege it again. The crash happens when AI is re-sieging "now-Beni Zilal" location.