Playlist made on laptop is only a truncated version on iPhone

I have Apple Music, a MacBook and an iPhone. I made a playlist on my laptop from my Music library. I opened the new playlist on my iPhone and only the first three songs were shown. I turned off sync on my iPhone then turned it back on. All the playlists disappeared, then reappeared, and the new playlist still just had three songs on it. I went back to the laptop and found the new playlist there had been shortened to just the first three songs - all the rest of the playlist is gone. What did I do wrong?