When starting a new playlist, often times the name disappears in the dropdown list. The work around I use is to start playing a new playlist, then go back to the song I want to add to the new playlist. Usually the new playlist is visible if another playlist is active. Not a big deal but annoying. My lesson is: if a playlist is playing, you cannot add new songs to it.
Hello @steveofstonehenge, can you make a screen shot of what you are talking about? This would be really helpful.