I’m using a new install on a pi 3b and spotify connect plays fine but if I select a new song from the playlist the current song just restarts instead.
Clicking next/previous in spotify on Windows will skip tracks as expected but a direct song selection doesn’t work. Also noticed that shuffle was on but when turned off it remained on with spotify connect so clicking next track played a random song instead.
Have you upgraded librespot? The version that ships with PiMusicbox is very old, I’m surprised it still works at all. The easiest way to upgrade is described at https://github.com/pimusicbox/pimusicbox/issues/523#issuecomment-495949590
That did the trick nicely 
Many thanks.