Googling that error message gets me this Qt bug report:
https://bugreports.qt.io/browse/QTBU...iewStatus=Open
Which only hits KDE and seems to involve Icons.
That specific error message is generated here according to google:
https://code.woboq.org/qt5/qtbase/sr...riant_p.h.html
and again here:
https://code.woboq.org/qt5/qtbase/sr...riant.cpp.html
And here is a very simple standalone Qt program that can be built easily and shows the same issues via drag and drop of items with icons but only under KDE, otherwize the program works fine.
https://gitlab.com/bugpocs/WidgetListCrash
So the Icon is being stored in a QVariant but something is creating a bad QVariant type?