I had the same issue trying to recover a 7390 which started reporting unsupported changes after a firmware update to 6.06. Resetting to factory and picking a custom profile didn't help. I had to restore using the 4.86 recovery tool here:

 _b/FRITZ.Box_Fon_WLAN_7390.AnnexB.en-de-es-it-fr.04.86-18550.recover-image.exe

Fritz.box Wlan 7390 84.05.21.recover-image.exe