When trying to rebuild Alpha Base, I discovered an invisible barrier on the norther end by the north landing pad. It cannot be ground down. Save and reload doesn't do anything, and it has been consistent in three different game-plays (different game-starts).
The wall is apparently two parts, a north-south portion and an east-west portion that mostly follows the walkway north from the base northern lobby, along the metal walkway, and then turns west towards the landing pad.
There does not appear to be anything I can do as a player to remove it, and it prevents rebuilding the northern portion of the base.
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