Hey all. I have exactly this problem and converting svg to png does help, but I don’t want to do it after each app update. Could someone please point out to the relevant bug tracker issue to track, if any.
What is the program that is not displaying the icon correctly? The SVG file the program uses could be causing the trouble.
Otherwise, file a bug ticket under plasmashell.
If 20.04 - KDE Plasma task manager does not show some apps during loading - Ask Ubuntu is truly the issue, then the problem is caused by the app in question having a broken .desktop file. The solution would be to report the issue to the app’s developers.
Which app is affected? Can you attach its .desktop file? It should live in /usr/share/applications