Shared playlist of imported music to family member's account shows no tracks

I have some home-made music tracks that I've imported into my Mac using iTunes. With iCloud Music Library turned on, I can sync a playlist of these tracks to my iPhone, and then download and play them from my phone just fine.

However, when I share the playlist with a family member who's part of my Family Sharing group, they can get the playlist, but when they hit 'Add' and it's added to their music library, the playlist is empty.

I have tried turning iCloud Music Library off and then back on on both my Mac's iTunes and on the family member's iPhone Music app in various combinations, but the result is the same each time: the playlist can be shared and will appear, but it appears as an empty list on my family member's version.

Anyway to get this to work?

BTW, playlists of tracks from Apple Music, of which I subscribe to do not have this problem -- only playlists of imported tracks, like from CDs I own or home-made music.