If you send the same message over and over, or send messages too quickly, YouTube will "ghost" your comments. This means that they email the video owner the comment, but never actually leave the comment on the video.
To make sure that your comments aren't ghosted, we recommend you have at least 30 different messages (don't worry you won't need to type in 30 messages, our spintax tool will help). If you are running a Share Video or Playlist campaign at the same time as a Comment on Video campaign, we recommend you have at least 30 variations of the message on that campaign as well.
If you have any questions, please let us know.