I have a friend (not local to me) with an iPad mini4. She had a problem with the iOS 11 upgrade and tried to roll back to 10.3.3 using the method found here: [Tutorial] How to Downgrade from iOS 11 to iOS 10.3.3 using iTunes She's getting the message that factory restore failed. And also an unknown error has occurred (3503). Unfortunately, there is no Apple store local to her. She's spent a good amount of time on the phone with support but they aren't having any luck either. Support wants her to keep trying to d/l restore image. Any suggestions as to a course of action for her?