When I install Spotify through snap on Xubuntu 18.04 the Spotify- icon isn't there. Instead it's the usual symbol for missing icon (the box with the red circle inside on a black background). I guess it might have something to do with the snap-package, but I don't know.
Just to clarify, I mean the Spotify- icon in the plugins menu, which appear when you click the plugin-icon in the notification-area.
Resolved with this commit: https://git.xfce.org/panel-plugins/xfce4-pulseaudio-plugin/commit/?id=c0ee99f46b8a8e46fc35191f64fd944dfbaa2ae7