My laptop sports COMODO antivirus (PoS!!!). After some digging, I found the Factorio executable in the list of the blocked executables. I guess this terrible antivirus blocks any kind of I/O operations of all blocked executables, so that no there was internet access for Factorio (hence SteamAPI ...

I have a couple of recent savefiles from the last two days but I am not able to see them under %AppData%\Factorio\saves. All of the savefiles up to November 1st are there, but not the most recent ones in the following two days. I'll list other aspects of this extra weird issue in no particular order ...