I ran into a problem today, when in spite of my media volume turned completely up, none of my apps including games, music, and Waze , wouldn't sound through the speaker. Ringtones and notification sounds did work, so my speaker wasn't broken.
I rebooted my phone twice without any luck. Finally, I looked at all the apps in the recent app drawer and found 25 apps there. I closed them all and reopened the apps that didn't produce any speaker sound before; now they did. So rebooting the phone doesn't clear out the recent app drawer. Why manually clearing them out helped fix my media sound, is something I can't explain. Perhaps, some speaker driver in one of the apps in the recent app drawer got turned off.