Save file reverted to significantly older version (PC/Steam)

Platform: PC

Yesterday, when I started the game on my main Steam account, I was presented with the EULA, Anon. tracking and crash report popups again. (I’ve played since the last update, when those also came up.) After accepting and getting to the menu to select character, I noticed two of my four characters had been regressed in level. Recently I re-rolled two of them and had been levelling them up, but all characters were level 31 before the issue occurred. Now, one was at level 26, the other 30. Meaning, a very significant amount of progression loss - probably somewhere between 6 and 8 hours worth. Considering how much loot I gather in my sessions, a good chunk of that was also missing (obviously).

I did recently log into my alternate Steam account to play around for a bit with the characters on that. Because I had not yet logged into that account since the last time I had to reinstall Windows and Steam, I didn’t think too much about it when that account prompted me for EULA etc. But getting the popups again on my main account yesterday after logging back to that one, I figured something had gone wrong.

What really puzzles me is just how far back the save file had been rolled. I was under the impression that the backup was supposed to be updated frequently, far more than just once every 6 to 10 hours worth. So this leads me more to believe that there is an issue with Steam sync and using more than one Steam account on a particular PC. I am stating backup saves here in particular, as nothing else would really explain this kind of rollback. Even though the main save should not have been an issue to begin with.

This is probably the second time in total I’ve had some kind of lost progress / reset, in the 670+ hours I’ve spent in the game. So overall it’s not horrible. Though any loss of progress is obviously bad. The first time I lost some progress was well over a year ago, on my alternate account. I cannot really recall any other details about that incident, other than it also pertaining to having signed in with two Steam accounts on the same PC.

Steps To Reproduce:
I guess the only way to attempt to reproduce the issue, is to make some progress on one Steam account and then log out / into another. Play on the other one for a while, then switch back to see if it causes any issues.

Images / Videos: N/A

Host or Client: N/A
Not really relevant, since it was apparent from just starting the game that something had gone wrong. Though mostly I am the host, playing solo.

Players in your game: N/A

I doubt specs has anything to do with the issue, especially since the most recent incident and the first one way back occurred on two significantly different PCs. The only common factors would be the game running from a SSD, using Intel CPUs and nVidia GPUs. (The first PC it occurred on technically does not meet the requirements for the game, but is still capable of playing on low settings.)

Might have been steam cloud save.
But the actual save folder path is your steamID.
So there should be 2 totally different saves.

Both accounts use Steam sync and yes, I know the saves use SteamID64 as the folder. Which is why it is so strange that signing in on the second Steam account would even prompt the main one to restore from Steam cloud - if that is whats happened here, and for some reason Steam had only synced that old save and failed since. Though Steam usually doesn’t give much error messages if it fails to sync saves, from what I’ve seen before with other games. Curiously, when I looked at the properties for the game after the incident, Steam was listing about 4mb used for cloud saves and 1mb free (approx). Now, after having played for a bit and Steam seemingly is syncing as it should, it is showing 8mb used (twice what it was previously) and 1mb free. So it stands to reason one of the save files wasn’t on the Steam servers at all, however that happened. (The main save and the .bac file are 4mb each)

Ultimately, I do not know if this is solely Steam’s fault, or if there is an issue with the game as well. Obviously, the local save files for the main account were still present on the PC and it really shouldn’t have triggered a restore from cloud, overwriting the local ones, when I logged back in. If Steam really had failed to sync previously, then the cloud saves would have had an older timestamp than the local files anyway and therefore should not have prompted a restore to begin with. So the whole thing is really strange.