It is possible, maybe even probable, that it is the "Screen mirroring" function that is causing the problem.
To turn it off go into "settings" on your Roku and then into "system" and then scroll to "Screen mirroring (beta)" and then press "OK" and choose "Disable screen mirroring."
I think for the YouTube channel to be causing the problem you would have to have the offending devices actually paired with it and the YouTube channel would have to be active on your Roku.
Two Roku Ultras, three Roku 3s and a Roku 1
"Part of the secret of success in life is to eat what you like and let the food fight it out inside." Mark Twain
Van Roy's Law: An unbreakable toy is useful for breaking other toys.