I’m experiencing a sync issue as well with the 2.2.8 software update. I get the same issue whether I’m using airplay on my iphone or ipad. I will watch for say 25 minutes, and some other undetermined amount of time and the AppleTV will ask if I’m still watching. This did not happen to me on 2.2.6.
I think I have a 3rd generation AppleTV. The generation just before the new one if that matters.