1. MusicBee sync the playlist into the folder "PLAYLIST" in the phone. You need to include this folder in your music player scanning.
2. I also had another problems with Windows 10 Store edition, very slow in copying playlist. I decided to install the desktop version and when I run the desktop apps, my antivirus complain MusicBee trying to change my protected folder. I set it to allow change and the desktop app
copied the playlist very fast, no hiccups. I wonder whether that's the root cause for the Windows 10 store version.
3. Another problem I have at the moment is all the playlist are incomplete. E.g. I have 50 songs in one of the playlist listed in MusicBee but same list only appear 47 in my music player.