Here they are, in all they magnificant transparency, yet solid presence, two gabion modules ghosts. In the begginnging I though I had somehow missed the spot. So I tried to fill it, only to find that, the spot in question was, somewhat obstructed. I then thought that maybe the terrain had strange irregularity caused by the flattening and made it impossible to build upon. So I put another gabion in front of it. After some time managing in other parts of the colony, I discover even the second gabion disappeard. And that the terrain is obsttructed. "I give up!, I have better things to do than to worry about Schrodinger's gabions!". until i find out that they, in the end, got built.... If you want I can attach a save file, but I don't know how can it be of any use, since the problem resolved itself and i don't know how to replicate it...