Some videos are age restricted and have embedding disabled:
https://support.google.com/youtube/answer/2802167

BrainzPlayer currently doesn't detect these are not actually played and as such still submits them.

Example:
https://musicbrainz.org/recording/77176b8e-9157-488d-a9c6-5f0d61c336c4

Also, since autoplay has been disabled ListenBrainz will still continue to advance to the next track(s) and happily submit each one despite not a squeak being heard.