Copyright of the stock media.
Because we don't create the songs ourselves and instead purchase the tracks from other composers, other parties may have the copyright on the material. In some cases, they (wrongfully) choose to enforce that on YouTube.
Unfortunately, these claims do sometimes happen. It's not something we are able to prevent, but we can help you get the claim released. The claims come up from time to time because Youtube has an algorithm that searches all videos hosted on their site for registered copyrighted music. Once the algorithm finds copyrighted music in a video, it places a claim on that video, assuming that the user does not have permission to use the music. While this policy does protect artists from improper use of their copyrighted material, it does not account for youtube users like our customers who actually do have permission to use the music.