I've had this problem before when I first got my S6. I phoned Samsung for help and they remotely accessed my phone to see what the issue was but was unsuccessful so advised a factory restore. This fixed the problem but only for a short time. As it had happened again and I was within the 28 day period I was given a new handset. I've had the new handset a month and this problem has just occurred again. Not sure if there is a fix out there for it other than restoring your phone to factory settings. I will be contacting Samsung again tomorrow. Sorry I can't be much more help.
