This might help use narrow it down, I'm with the vlandians it seems too be everytime I try too seige a sturgian castle/settlement or a battanion castle/ settlement
This Same bug is happening too me on the Xbox One S, on my playthrough everytime I go too seige a castle one I press attack the loading screen comes up and then the game just crashes with everysingle seige so I end up just having too auto resolve the seiges so the game doesn't crash