Comment # 3 on bug 1047849 from Wolfgang Bauer

(In reply to Frank Kruger from comment #2)
> The icon is displayed correctly under "Utilities" and in the search result.
> Only "Favorites" are affect. Deleting icon-cache.kcache and logout/login
> does not change anything.
> 
> I am using Breeze Dark

I think it's a "bug" in the "Breeze Dark" icon theme then. The Favorites use a
bigger icon size than the regular entries, so probably only certain sizes are
affected.

> (on Tumbleweed I do not experience this issue).
I cannot reproduce it here either (42.2 with the latest packages from
KDE:Frameworks5).
So probably it got fixed already in later versions.

> With Breeze the icon is displayed correctly also under Favorites.
Even more indication that it's a problem with the icon in "Breeze Dark" itself.

You could try to install Tumbleweed's breeze5-icons package on 42.3 to see if
it helps. (shouldn't cause dependency problems or break things, after all it's
just an icon theme...)