How to get rid of duplicate / not working app icon

• Find the relevant .desktop files on your system with the command

  find / -name '*.desktop' -exec grep -H "Name=Spotify" {} \; 2>/dev/null
  

• Inspect the contents of the files you found. Look at the Exec= line to learn which executable they are calling. That the icon is in the application overview indicates that the executable is present.

• Try each of the command after Exec= of the different launchers on the command line. One will not work, the other will.

The issue indeed may be a faulty installation. First try uninstalling the faulty application: that will automatically remove the .desktop launcher. Manually deleting the .desktop launcher also will eliminate it from your overview, but prefer to remove the faulty application in the first place.