This happens when I open a project with all frozen tracks and without doing anything else select Share -> Song to Music ... in the menu. Logic seems to bounce it and export it to Music, but it results in a totally silent file with the correct song length. Unless I play the song briefly and do the same, then the song is exported correctly.
The whole thing doesn't happen if the project doesn't contain frozen tracks.
macOS 11.6.2 (20G314)
Logic Pro 10.7.2