I'm not playing experimental. I have 2 save files/worlds, 'first game' and 'World 2', and the autosaves corresponding to each file/world. When I started playing tonight, I was prompted to cloud sync and so I did, as what happens each time I start up. My 'first game' and it's autosaves were successfully imported but I lost all of 'World 2', the save file I'm currently playing most of the time.
There were 2 folders in the SavedGames folder, common and a folder named as a long list of random characters. The common had all my 'first game' files, and the second folder was empty.
The SavedGames_Bak folder had an old version of World 2 so I didn't lose everything but lost a day's worth of playing. I also had an even older backup I made myself.
When I finished my last session I briefly loaded into my 'first game' save before I closed the game. Not sure if that had anything to do with 'World 2' disappearing.
In the mean time I guess I'll just do manual backups everytime I have a session.