I recently went bananas trying to place pillars and ceilings in Hidden Lake for my base. I couldn't place a number of them which restricted the size of the base (not a huge problem) but having played Ark since it's first week of early release, and having used S+ extensively as well, I could not work out why these structures wouldn't place.
Fast forward to today, and I tried to place a metal box where a supply drop falls so that I can collect resources from other maps and transfer them to a box from the supply drop, in the comfort of my base. I could not place anything - boxes, pillars, foundations.....
Did some research and found that PvE has building at supply drops disabled, so people cannot box them in I guess. The commandline to undo this is ?PvEAllowStructuresAtSupplyDrops=true. Having always played PvP this was new to me.
I am not trying to change this (although that would let me set up my drop box

Cheers
Datto