MusicIP "M" mix button

I'm not sure what the little buttons (typically play, remove, and M) next to song titles in the LMS web UI are called, but a long time ago there used to be an M button which allowed me to create a MusicIP mix directly from the song list. At some point M became "More" which would bring up the details view for that song on the left. Later the MusicIP interface somehow became a sub-interface in the left menu (that is similar to a regular song list, but generally with fewer buttons) but in that interface the M button returned with the ability to make a new MusicIP mix from that song.

This button seems to be missing in 7.9. I'm not sure whether it was something I enabled in some plugin or interface setting, but I would like to get it back. Does anyone know if its possible?

TIA