Given Build 417.2 and using 'plasma-discover' from the console gives:

QQmlApplicationEngine failed to load component
qrc:/qml/DiscoverWindow.qml:194 Type DiscoverDrawer unavailable
qrc:/qml/DiscoverDrawer.qml:71 Type SearchField unavailable
qrc:/qml/SearchField.qml:26 Type TextField unavailable
file:///usr/lib64/qt5/qml/QtQuick/Controls.2/org.kde.desktop/TextField.qml:-1
Type MobileTextActionsToolBar unavailable
file:///usr/lib64/qt5/qml/QtQuick/Controls.2/org.kde.desktop/private/MobileTextActionsToolBar.qml:60
Cannot assign to non-existent property "icon"

Errors when loading the GUI
Could not open the AppStream metadata pool ""
invalid kns backend! "/etc/xdg/ksysguard.knsrc" because: "Config group not
found! Check your KNS3 installation."
invalid kns backend! "/etc/xdg/servicemenu.knsrc" because: "Config group not
found! Check your KNS3 installation."
Discarding invalid backend "ksysguard.knsrc"
Discarding invalid backend "servicemenu.knsrc"
setting currentApplicationBackend PackageKitBackend(0x5599332be3b0)