The issue itself happens when Plasma falls into software rendering mode, for example due to a hiccup in the graphics driver or a issue with QT (sometimes just because Plasma is a diva 
). However, the effects are completely different - ranging from incorrect display of a single widget, incorrect display of individual applications, missing panels and wallpapers to a completely lame and unusable plasma desktop. Two simple examples:
Sometimes the âQtQuick Renderingâ dialog is displayed in this case, but not always.
Either you set the settings to automatic when the dialog is displayed or you delete the two corresponding lines in the kdeglobals if present. You can also call the QtQuick render settings manually:
kcmshell6 kcm_qtquicksettings
This setting is part of the KDE âSystem Settingsâ, but is not officially displayed in these. Some of the settings are not (or no longer) displayed, but the modules are still available. You can list all modules of the KDE âSystem Settingsâ with:
kcmshell6 --list
And you can call up the individual modules with kcmshell6 <module name>, for example the deprecated âBackground Servicesâ module:
kcmshell6 kcm_kded
/offtopic