Failed to upload several save files

I had a connection issue yesterday evening, I barely was able to navigate to menu and exit the game as I always do. Then I ran my save backup script and I have noticed that several save game files were not there (404 error).
I am downloading the save game files straight from my steam profile and I do it after 4-5 hours of gameplay in any long open world game (this time it was Blood of the Dawnwalker)

I have lost completely save game files before in stores like Epic Store but this never have happened to me before with Steam.

In order to solve the issue, I have identified the save game that is corrupted (looked at the png picture) and opened a working save and just overwritten the corrupted one.
Then I have re-run the script and all of the files were downloaded successfully.

Lesson from my experience: Backup your save files. This can happen even with the most reliable game store such as Steam.