I had one small but frustrating glitch last weekend, that could have been related to a firmware update on my processor. I lost the center channel on one single program
that I had paused,
and all my standard "fixes" didn't work. I played other shows. They had no loss of the center channel. I changed the processor's mode from Auto to Reference Stereo, played a few seconds, then returned to Auto. No fix. I restarted the AppleTV (actually, AppleTVX). Still no center channel (no dialog.) I restarted the processor and televsion - fully powered off, removed the power cords for a couple minutes, fired 'em back up. No joy.
Basically, I moved on to something else, and when I returned the next night and picked up the show again, it was working fine.
But... I don't know if that was an ATV(X) issue or a processor issue, and I suspect the latter more than the former.