Publishing administrators handle the administrative side of music publishing—like registering your works with performance rights organizations (PROs) and mechanical rights societies (like The MLC). They don’t own your songs, but they usually take a share of the royalties they collect on your behalf.
Examples of publishing administrators include Songtrust, Sentric, vCD Baby Pro Publishing, TuneCore Publishing Administration, and Kobalt.
If you have a publishing admin deal in place, that company is the one responsible for fixing any issues related to publishing or performance royalties.