I’d lean towards Roku. I think they are starting to examine the actual VIDEO OUTPUT of your TV, and collecting information on that and sending it to their advertisers.
Since your IP might now be associated with watching a certain movie, advertisers can purchase IP-based advertising, which would explain how Youtube could pop up ads for the exact movie they associated with your IP.
Addendum: As oddly as Plex has been making app decisions lately, I still seem to think that our own server contents are not being leaked outside. Most likely, those account settings you see are for Plex’s own free streaming services, and they really want to be able to sell what stuff of theirs you watch.
