Trouble with Desktop-Icons

[René J.V. Bertin]

>I use openSUSE Leap 42.3 Plasma and the Oxygen Theme. This is not acceptable
>and scares every new user who uses KDE on Linux.

I agree but must point out that this also happens on MSWin and even on Mac (though it hasn't happened to me there for years).

I've had it on a pre 14.3.x Plasma4 desktop, and got the impression then that it helped to lock the icons in place.

>To reconstruct the icons I copy a saved version from .config/plasma-org.kde.plasma.desktop-appletsrc
>and login again. But this does not fix the problem until the next login.

What you can do is run a script that restores the file at some appropriate, early-enough moment. That could be your .login script or a plasma startup script, or even through xinit.

Good luck...