The status is tracked at your server. Let’s see if it’s working.
Start playing something in Web, anything. Then jump to 10 minutes. Let it play for a few seconds then stop it. Then pull up the XML for that video and post it here.
Then play that same video from the Apple TV and do the same. Grab the XML and post it again.
You may need to make sure you stop the playback on one device (not pause), before you play on a different device.
otherwise plex can think that the first device is still playing.
also, if you have any device that has something paused, it can block playback tracking to other devices. (like a family member pausing a movie on a tv, then you try to watch same show on a different device).