I red carefully what you said, but I affirm that it worked for me. I installed first the original 5.3, just to see if we could play (I was stupid) then the mod 5.2.2, and after mod 5.3
Version 5.2.2 is only usefull to get the save from FB, then you need 5.3 to load the save.
Loading your save in 5.2.2 is impossible in ALL cases since the update, but you have to look, and recognize your save ID up right on the loading screen. If the account is linked, you get your current ID, and not a new one for a new game.
The save ID tells you if you get your save or not! It's subtle...
Several people have managed to recover their backup on this forum...
I'm just saying that I'm not the only one to succeeded.
So, there is a way
But it's difficult... (Even for a Slytherin