I've read through the articles and did A LOT of testing. The problem comes down to the Facebook app and its handling of audio on your phone. The specifics are related to auto-play of videos and scrolling through the news feed.
Notice that any app that uses audio shows up in the tray when you swipe up on the phone? If you play a video from the YouTube app and swipe up on the phone, you will see the audio level and a long URL. If you play music from iTunes on the phone, the artist info and song info will show up in the tray. EXCEPT, when you play a video from the Facebook app, it DOES NOT show up in the tray.
So, the Facebook app handles audio on your phone like a notification, and when a notification is paired with audio, the native audio control on the iPhone drops your music/podcast volume by half (or to zero) to allow the sound of the notification to come through. This must be a bug with the Facebook app. I tried changing all of the possible settings in the app to fix the problem, but I had no luck.
The solution, delete the Facebook app and use Safari on your phone to access Facebook. Playing the same videos from Facebook through Safari will now show up in the tray with the url string.
Hope this helps someone. We need to direct this attention to Facebook support and not Apple support. It's not Apple's problem.
Also, I think it's safe to say that any app that handles audio playback like a notification will cause this same problem to occur.