I am also having this problem with followed playlists. We have a family Music Unlimited account with multiple members in our household. I bought the plan thinking we could each have our own playlists and we could each play our playlists anywhere in the house. Apparently not.
Since all the devices are registered to me, I had my husband share his playlist with me and I followed it. I can play it through the Alexa App, or on my laptop using the Amazon Music site. But Alexa won't play it. She finds the playlist, says she's now playing the playlist, but then plays nothing.
What's the point of a shared family plan if we can't really share it?