I've discovered the issue! ..or rather Schumami guessed at it correctly.
As soon as I move the save folder out of my user directory (in Windows, C:/Users/User_Name/ it cannot create the directory!
So since I immediately knew that I wanted to put my Autosave folder on my non-Windows drive, under F:/Images/GIMP_Autosave it simply never worked from the start.
As soon as I move the save folder out of my user directory (in Windows, C:/Users/User_Name/ it cannot create the directory!
So since I immediately knew that I wanted to put my Autosave folder on my non-Windows drive, under F:/Images/GIMP_Autosave it simply never worked from the start.