Missing icons

I upgraded to Leap 42.2 yesterday. I run kde display manager and fvwm2 window manager.
Most things work fine except that the icons have disappeared. In particular:

  • emacs toolbar is grey and transparent. The icons are there, but invisible (already noticed in another post)
  • dolphin window displays no icons, only text. While starting dolphin the console says QPixmap::scaled: Pixmap is a null pixmap
  • KDE system settings (/usr/bin/systemsettings5 ) displays only 3 icons. The remaining setting options are displayed as text only.
    However, they are usable.
  • Applications that take care of their own icons as firefox or gimp have no problems.
  • My own application that fetched icons at /usr/share/icons/oxygen/32x32/ could not find a couple of icons, but they could be found
    at /usr/share/icons/oxygen/base/32x32/

Any suggestions?