Audio sync issues

When using Xfinity Stream, the audio slowly starts advancing ahead of the video playback. This happens with recordings and live playback. It seems to be happening much more frequently. I have cleared the cache, cookies, etc from my browser and it makes no difference. I have logged out, restarted my computer and no luck. At best it will be synced when I resume playback, but within five minutes or so, the video starts falling behind. This doesn't occur with ANY other video playback service, not Vudu, YouTube, Hulu, Amazon etc, only Xfinity. Any advice would be helpful....