What I do:
1. Open JRiver (using remote Library Server)
2. Create, then rename new playlist
3. Drag&drop some songs to the playlist
4. Close JRiver
5. Open JRiver and there's no my playlist

I can't find any save button, I thought it should be saved automatically. ?
I use 19.0.32 now but AFAIR it happened with v18 too.