Please note that we've updated the Mount & Blade II: Bannerlord save file system which requires you to take certain steps in order for your save files to be compatible with e1.7.1 and any later updates. You can find the instructions here.
A part of the wall of Pen Cannoc is missing as you can see on the following screen :
The concerned wall is localized here (on the aim of the crossbow) :
At disposition if more information needed.