I have Echo Plus 2nd Gen and Echo Dots 3rd Gen. I found that setting up the Playlist is critical. Namely if the Playlist name is like an individual song in Apple Music, Alexa will play only the individual song, not the playlist of the same name. So when there is an overlap, I will name the Playlist with the prefix "My". If my Playlist begins with a song upon which the remainder of the Playlist is based, I must use "My".
I have Playlists that begin with a favorite song upon which Genius will create the Playlist. For instance I used the song "Crazy" by Patsy Cline to create a genius Playlist. If I say "Play Crazy", only that song will play. Upon naming the Playlist "My Crazy" and tell Alexa to play "My Crazy", the entire Playlist will play.
Basically my Playlists will be "My Jazz", or "My Classical", etc.. My command is:
"Alexa, play My Jazz". Alexa will respond with "Playing My Jazz from Apple Music".
Alexa is very specific, so if I hesitate, stutter or mispronounce, I have to start over. I hope you find this helpful. Good luck!