have you tried a restart of windows?
Try a clean boot and see if it changes anything - make sure to read instructions and make sure NOT to disable any microsoft services or windows won't load right -
https://support.microsoft.com/en-au/help/929135/how-to-perform-a-clean-boot-in-windows
if clean boot fixes it, it shows its likely a startup program. You should, over a number of startups. restart the programs you stopped to isolate the one that is to blame.
it could be an option in one of the programs
only shortcut keys in spotify that use shift are for volume anyway -
https://support.spotify.com/us/using_spotify/system_settings/keyboard-shortcuts/