This started for me when I installed Nougat. Just my ringtone would revert back to VZW Airwaves after a couple of hours and Wifi calling wasn't working. No fix available, so they shipped me a refurbished phone. I set it up and never installed new update (left it on 6.0.1). NOW RINGTONE AND NOTIFICATIONS SOUNDS REVERT BACK TO VERIZON DEFAULTS!!! What's going on? I've had the S7 for nearly a year and never had this problem.