Custom dock icon reverts to old one whenever the app is open.
I have changed the app icon for 2 apps (VLC and JustColourPicker) and it shows the new icon in the dock only when the app is not open.
However, as soon as I launch that app, the old icon reappears in the dock. When I close the app, the new icon appears again. I have tried replacing the favicon.icns file in the package contents but it still happens (not sure where it's getting the old image from if I've now removed it). I've also restarted the Dock and Finder several times.
Nothing seems to work, the custom icons only appear when NOT using that app, when you use it the old icon reappears.
Can anyone help?
(BTW It always shows the new icon correctly in Finder and Launchpad whether app launched or not - it's only the dock that exhibits this behaviour)
MacBook Pro 15″, macOS 10.15