Ok, I got what you mean now. Thanks for re-explaining it!
Unfortunately, I don't use any social media apps on my Note 4. I don't even email from it. So the only notifications I get is messaging... which of course uses just the one tone I chose for notification.
It's kind of curious that WhatsApp can choose a ringtone but not be able to play it. Have you tried copying the ringtone you want to use for WA and placing it into a different folder and have WA browse to that folder and choose it as the ringtone? I'm assuming maybe you're using a system ringtone for WA right now and maybe the system just doesn't like it since your current notification ringtone is being used system wide. Or, how about trying to select a song from your media folder as the ringtone for WA. I'm just trying to find out if something will work from a separate folder other than where the system gets it's ringtone. I'm just pulling at strings here!
You know, this post of yours has gotten 560 reads. You and I are the only participants. Hate to say it, but this doesn't bode well for another thread on the subject.