Unwanted controls on iPhone while watching TV

While watching the debate tonight on my iPhone Xʀ, control bars kept appearing at the top and bottom of the display for no apparent reason. I wasn’t even touching the phone. How can I prevent that? I haven’t seen that behavior on my iPad. They would go away if I touched the screen, but only temporarily.

We haven’t noticed this here, but we’ll see if we can reproduce this behaviour. Has anyone else seen this?