Working on a freshly updated re-install of KDE Neon, Plasma version 5.8.7, I could reliably crash plasma by right-clicking on the taskbar button belonging to an open application. It didn't matter if the app was minimized or not, and no debug tracer was triggered after plasma restarted.
After installing the kde-runtime package to obtain kquitapp/kstart (for another issue), I happened to trigger the crash while a console was open from which I had run 'kstart plasmashell'. The error message from KActivities said "Database can not be opened in WAL mode". It was evident that the database files in .local/share/kactivitymanagerd/resources/ were owned by, and only writeable by, root.
I cured the crash problem with

Code: Select all

sudo chmod -R a+rw ~/.local/share/kactivitymanagerd/resources/

This might help someone else in the future.