It happens once in a while in mine. The list will come back if you logout and login again, which requires touching a few buttons and you can't do it while driving. Became a habit for me to leave music playing when I leave my car, song will start playing next time I drive, if not, I know I have to do the logout-login exercise before I leave car park
Seems this problem was there since introduction of Spotify, hope they will fix it later