Same here

Any fix?

Have you ever served as a soldier under any lord in this particular campaign?

Yes

I'm currently sieging with 80 inf. 100 gunners in sandbox and the gunners are so buggy and do not follow commands, and they seem to miss more than 80% of their shots despite that not being the case in a regular battle. The castles are impossible to siege without brute force. No use of tactics can be made here- and it seems like they get stuck on the tight corridors and pathways causing them to just get mowed down by militia archers. I downloaded a mod 'Teppo Formation Fix' which separates them hoping it would fix something but... nah. Sieging is just broken with the new castles causing horrible pathing.