Hi Aryeh,
I was able to reproduce this in the BasicExample app (Swift). To reproduce this, I have done the following:
1) Set contentPlayer.allowsExternalPlayback to false
2) Launch app
3) Accessed music widget and connect to nearby device via AirPlay
4) Played the video
As a result, the ad will play on the connected device and the player on the phone will have the ad overlay (Learn More button, Ad countdown). Once the ad is finished, the video will play on the phone as expected, but I notice the "Linear Inline" ad on the screen of the AirPlay device is still visible and stuck at the end of the ad's video (where it says Linear Inline: 1 second). I attached a screenshot of the phone's screen for reference.