As the maintainer of Plank Reloaded, the most common bug report I get is "this app has the wrong icon." It's almost never the dock - it's a broken StartupWMClass.
thoughts.greyh.at/posts/startu...
thoughts.greyh.at
Demystifying StartupWMClass
Eventually, every Linux user opens an app and finds a generic placeholder icon staring back from their dock/panel. It looks like the dock is broken, but it almost never is - the cause is a single line...