Since in 3 of my last 4 Interior Settlement attempts this issue has come up, I can definitely say that this is TEXTURE issue! How come you ask? Because: 1. You can place items in Workshop Mode 2. You can use them out of Workshop Mode 3. Both in 1. and 2. they are invisible, while in 1. you can also see the outlines of object, in case you wonder how I placed them As a curiosity, I was able to place Turrets visibly while in Workshop Mode quite well in one of the problem interiors. Totally baffles me! Will now check if I can do same in other two Interiors, as if yes, that should give a clue as to what is going on.