SUMMARY
With no user interaction, Discover throws a "Packagekit stops running" message 

STEPS TO REPRODUCE
1. Start Discover on the command line
2. Wait for a while
3. Watch for error messages in the output

OBSERVED RESULT
After a while (30-40 seconds on my system), PackageKit seems to crash:

> plasma-discover
Cyclic dependency detected between "file:///usr/lib64/qt5/qml/org/kde/kirigami.2/styles/org.kde.desktop.plasma/Units.qml" and "file:///usr/lib64/qt5/qml/org/kde/kirigami.2/styles/org.kde.desktop.plasma/Units.qml"
file:///usr/lib64/qt5/qml/org/kde/kirigami.2/GlobalDrawer.qml:265: TypeError: Type error
file:///usr/lib64/qt5/qml/org/kde/kirigami.2/private/globaltoolbar/PageRowGlobalToolBarUI.qml:65:9: QML RowLayout (parent or ancestor of QQuickLayoutAttached): Binding loop detected for property "maximumWidth"
file:///usr/lib64/qt5/qml/org/kde/kirigami.2/private/globaltoolbar/PageRowGlobalToolBarUI.qml:65:9: QML RowLayout (parent or ancestor of QQuickLayoutAttached): Binding loop detected for property "maximumWidth"
invalid kns backend! "/usr/share/knsrcfiles/servicemenu.knsrc" because: "Config group not found! Check your KNS3 installation."
invalid kns backend! "/usr/share/knsrcfiles/ksysguard.knsrc" because: "Config group not found! Check your KNS3 installation."
file:///usr/lib64/qt5/qml/org/kde/kirigami.2/private/globaltoolbar/PageRowGlobalToolBarUI.qml:65:9: QML RowLayout (parent or ancestor of QQuickLayoutAttached): Binding loop detected for property "maximumWidth"
adding empty sources model QStandardItemModel(0x559698fc01b0)
QObject::connect(AbstractReviewsBackend, ResourcesModel): invalid nullptr parameter
org.kde.plasma.libdiscover: Couldn't find a category for  "fwupd-backend"
file:///usr/lib64/qt5/qml/org/kde/kirigami.2/private/PrivateActionToolButton.qml:77:5: QML Binding: Binding loop detected for property "value"
PackageKit stopped running!

EXPECTED RESULT
No PackageKit crash.
No or more expressive/helpful error messages.

SOFTWARE/OS VERSIONS
Operating System: openSUSE Tumbleweed 20201216
KDE Plasma Version: 5.20.4
KDE Frameworks Version: 5.77.0
Qt Version: 5.15.2
Kernel Version: 5.9.14-1-default
OS Type: 64-bit
Processors: 8 × Intel® Core™ i7-8550U CPU @ 1.80GHz
Memory: 15.5 GiB of RAM
Graphics Processor: Mesa DRI Intel® UHD Graphics 620