The key is to CLICK ON THE TITLE OF YOUR TRACK in the track section, you can NOT download your song from the TRACK SECTION (the list of all of your tracks) and neither from the PLAYER (the small bar at the bottom). In those you can only share, add to album, remix (both) and hide/unhide and pin (the list), but you can download the song from the track page (the page fully dedicated to your track).
How do I download the beats