This should be reported to FC forum, related to Qt5 & driver issues… it is not related to KSU code, but to pc drivers & Qt5 compatibilities.
I don’t know what has changed between FC 0.18.3 and 0.18.4, but on my PCs StepUp does work correctly with both releases.
Even FC0.19 is fine too.
duckduckgo search for ‘Unhandled Base::Exception caught in GUIApplication::notify.’