Any shared content or person hqave access to your pc or check login history and see if other have access to the account, i did not say this is it, but what else of crazy ideas do you want us come up with.

I doubt game devs had a issue, so only thing is left is someone start new game or delete it.

Technicaly steam cant delete newest time stamp you once backup. this is know as sync to newest files, what ever that has newer time stamp on steam cloud server or your local files.

This is why family shared content or other user have access to you pc come in our minds here.

im sure you can see why we think this, problem is i cant see any other have seen this before, not as fare as i know.

åps.
we are not steam support,we are steam user just like you, and try explan what if this and that situation here.

Steam login history ( they have change this info ) require login and security.check.)

https://help.steampowered.com/en/login/?redir=%2Fen%2Faccountdata%2FSteamLoginHistory&need_password=1


ps.
I dont think we have seen steam user claim steam delete data ever, somehow this only happend doing hard drive crash, but this dont look like that issue at all to you,

Make sure you have 200gb+ free storage space so windows do not do a recover free space and other things MS can do, this is why you dont see crash OS anymore, but also has a consequence for recover MS OS script that kick then system is in trouble.

This dont lokk relevant to you, but we cant say here what happedn at your pc, if drivers was full.

ps.
PPL from the past in win 7 or lower know this never use all space, know as last 10% rules with red label hard drives, but today its removed with TB drives you cant use 10% on 10TB drives. ( same goes with lesser then 250gb SSD boot drives.

All them issue, don't help with next gen games way past 100+gb installation.
200gb free is not enough with them games.