Hi folks,
I also am having this problem.
Sounds work on my speakers (i.e., alerts), but iTunes, videos, etc., do not work.
I have my mute unlocked. There flat out isn't a sound bar to adjust - it just appears as an empty bar with no ball to slide up or down.
When I put my headphones in and pull them out, my sound bar will return and it will work, but if I try to adjust it, it will disappear again and the sound will become totally muted.
If I double tap the home button and slide the bar over, I can restore the audio if I mute and unmute using the mute button on the right side.
And, yes, I have closed all apps and rebooted the iPad.
Should I be taking this to a Genius Bar?