Have you tried turning the volume up while in the app?

 

That shouldn't be possible at all, unless you have root. Even then it can't get those permissions unless it asks through SuperUser.

 

I had the exact same problem as you vandyman. Sound was fine on ringer and notifications, but no sound for apps etc. from the rear speaker. They were working fine through headphones though. I even did a factory reset and that did not fix it. It fixed itself overnight though.

I thought it might have been water getting into the phone when I put on a wet apply screen protector since it happened at the same time, but it seems other people are having the same problems without the water.

I hope its just a software issue!

 

Checkout Volume+ it helps with the weak volume levels on the GN