I just played GZ on PC and when I decided to fast travel to the base it was ALL gone. Not just the base I built, but the truck and the radio units as well.
The markers to choose difficulty is there, albeit floating in mid-air.
Travel to the other side of the map and then travel back, that should fix it
I just got this bug.
I was at Himfjall island and fast travelled to the base, everything was gone and stayed gone.
I fast travelled to the nearest place (Hikers barrack) and went on foot to the Base location.
It was all there again.
Weird bug, but at least for now we have a temporary fix.
In the last week I noticed that many ammo-boxes and similar were gone on first look, too… But after looking in another direction and turning back they suddenly were there… Maybe the game is getting problems loading all the needed objects fast enough.