Bought new SX Max and traded in X on launch day. Several times this past week when went into messages and some apps back button or done button would not respond. Only way to correct it was turn phone off. Even did a few hard resets and things would work fine for a while. I restored over WiFi when got phone and after speaking with an Apple rep he made a suggestion that I backup and restore connected to computer. Did this last night and seems to have fixed the issue. I have always upgraded over WiFi, however, in the future will probably connect to computer. Was quick and flawless.