Made some maps in v1.2 64b Windows 10. Used the flat ground map as well as some other hilly ones. Built a whole bunch of stuff on them and saved, thumbnail of the save shows the ground properly. Updated to 64b v1.3 and loading up those saves has the ground disappeared. All my stuff is just floating in nothingness. Tried to "replace" the ground by selecting the ground base I wanted again, but it spawned that in as a fresh base and deleted everything I built.  Went to manage, check for updates and I'm up to date. Persists through game restarts.

 Oddly it didn't affect maps I had made in 1.2 that were more or less the randomly generated ones. The ones with missing ground have buildings on them. 2 are cities with city walls and houses and trees, 1 is a camp scene with tents, archer towers, and a fire in a forest.

Any idea what happened or if this is recoverable?