These 2 methods work on my Clip Sport (non-plus version).
Settings -> Music Options -> Shuffle = On
OR
Music Menu -> Playlists -> select a playlist -> select any song to play. Then, while the song is playing, press the Option menu button (below the large oval Select button). Then select Shuffle = On.
The Shuffle selection will remain active during subsequent music playback from the Music menu, Folder menu and Card menu.
