Same here. The case stopped working today 08.09.2018 in the afternoon. I am from Romania. I will contact support regarding this issue but I don't think that I will get some help.
Per the Samsung Support desk, just turn the phone off (Power Off, not Restart) then power on - works perfectly now.
Such a simple fix; I apologized to the Samsung Help desk for wasting their time with such a simple problem with a trivial solution.
Mine one has gone the same inside a year!! I've tried all the holding keys down, re booting etc but nothing helps. Its driving me mad. How can it be fine one second & not working the next? Grrr. ☹