Hello,
I just found this thread. It's the only issue I've been able to locate that's similar to my own Facebook app notification sound situation. I realize this isn't the Samsung section and that my issue isn't identical to the OP's. But I'm hoping it's close enough to include here and that it may elicit some thoughts and insight.
My phone is an S7 edge. It recently arrived back from the Samsung repair center for a warranty replacement of a failed display. When I shipped it out, its OS version was Android 6.01. Naturally, when it returned it had been updated to Android 7.0.
At some recent point, my Facebook app auto updated to v132.0.0.20.85 and I've noticed that I'm no longer able to get my choice for a ringtone to *stick* as FB's audible notification event sound. The Notifications > Ringtone menu items are indeed there and I can select any ringtone from the list that appears. But my selection will only last until the phone is restarted or until the Facebook app is otherwise stopped and restarted. Once that's done, the FB app always reverts back to the 'default notification sound' for some reason. It never used to do this and I'm unsure whether it's a bug in FB's recent update or a firmware or hardware related problem.
Any thoughts will be appreciated. If necessary, please move this reply to its own thread in the Samsung section. Or I can always start a new thread there as well.
Thanks in advance.