I also have an issue - somehow iMazing restore does not work on my Ipad.
After doing everything the way I was supposed to, iMazing claims that the backup was restored but after loading the game, nothing changed.
After some tests I found that the restore backup function basically does nothing on my device. I can create backups, edit them and use the restore function but after restarting the app on my Ipad is in exactly the same state as before the restore. So I guess iMazing has some problems either with 12.3.1 or with the app restore function in general.
If anyone has an idea what I could try, I would be very grateful.