Why did third party app notifications all revert to tri-tone, and how can I fix it?
This is apparently a bug in iOS 10, based on a page I read the other day that I can't find now. For me, it's resolved every time by doing a hard reset on the device (hold Sleep + Volume Down until the Apple logo appears). I had this problem on my iPhone 6s, too, for the couple days it had iOS 10 on it before I got my 7.