The THRiVE headphone jack is apparently very sensitive and any spec of dust can activate "headphone mode." If this happens to you, you will hear notification and alarm sounds from the speaker but the speakers will not play any audio for video, games or music.
Below is a quick and easy fix - Worked for me.
1. Power off and remove battery
2. Spray some "electrical contact cleaning solution" into the headphones jack (available at any hardware store)
3. Plug in and out head phones jack a couple times (so that the solution touches all internal components)
4. Spray some more "electrical contact cleaning solution"
5. Plug in and out head phones jack a couple more times times