I have this problem with a base build on water and a base inside a building. Even if cursorTarget (text appears showing wall type & fortification) is at the wall, special actions won't appear. This seems to related walls/doors overlapping with water/structures and even other walls. Sometimes you are able to find some area to lock/move/remove but not always.
This came up with the new Exile version and affects both DEV and Apex preview at least.