My outpost and everything I own is gone

[Solomon]

It has happened twice on this save file. I build an outpost, leave, come back and it is gone. My map says it's still there, but it is not. I had some guys in cages there, who were suddenly free, and I saw them crawling away when I got back. All chests are gone, all buildings, all items. When I load my game it says I should upload my zone files, but I am unable to figure out where I am supposed to upload them. I tried attaching them as a zipped file to this post, but it says the file is too large.
How can I fix this?