After I upgraded all system monitoring widgets are empty/blank
I had different widgets for, Network Load, Disk Load, Memory Usage, CPU Usage.
It seems these are now all one new and the same widget. Previously they where a separate widget for each (at least it appeared as separate widgets).
Now it is System Monitor Sensor Widget.
I have tried every conceivable configuration options for the widget, nothing is displayed on it.
KDE Plasma 5.18.90 updated from the KDE repositories:
http://download.opensuse.org/repositories/KDE:/Applications/KDE_Frameworks5_openSUSE_Leap_15.1/
http://download.opensuse.org/repositories/KDE:/Extra/openSUSE_Leap_15.1
http://download.opensuse.org/repositories/KDE:/Frameworks5/openSUSE_Leap_15.1
http://download.opensuse.org/repositories/KDE:/Qt5/openSUSE_Leap_15.1