First, if you have any non-standard plasma widgets, I would try to remove those.
Then, I would kill
plasmashell process and then run it from the command line to see the full debug output.
to get a useful backtrace you need to install the *-dev related packages.
potentially removing your whole panel, or widgets on your background and recreating a new panel if you want. is an option.
finally, you could inspecting your local plasma related config files.
$ find .config/ | grep plasma
you could back them up and move them away between restarts. I would start by
hope this helps