I use Kubuntu and I like to use something similar to Quick Launch from Windows XP. There is this panel where I put my icons via the Plasma menu (whatever it's called), right clicking on the appropriate application, and then selecting "Add to Panel (Widget)" (as per this answer).
As you can see in the image above, for a long time I've had this issue where the icons occasionally disappear. I'm pretty sure they are the ones managed by the Snap package manager, and they seem to disappear when the respective application is updated. The icons do keep working when the invisible icon is clicked, but not being able to see the icon is distracting.
So far, I've had to tediously edit the panel, remove the icon, close the panel, add the icon back to the panel, edit the panel again, move the icon to the right place, and close the panel again.
Does anyone know how to fix this annoying issue?
Operating System: Kubuntu 20.04
KDE Plasma Version: 5.18.8
KDE Frameworks Version: 5.68.0
In /snap/packagename you should find the icons (*.png). Copy them to the desktop. Then rightclick the bar to adjust the settings and drag the icons to its place. Delete the 'empty' ones.
Have had the same issue, and solved it this. Had the issue in the launcher menu as well.