I have pretty much the exact same problem as discussed here. Re-posting this as a separate question since I can't comment and was advised to do so.
For me, the crashes happen most often when I hover the mouse over a panel launcher that has an open window. This is almost guaranteed to crash Plasma with the same dialog as shown in the linked question.
I've tried Aidan's suggestions in his answer to that question and will wait a week to see if that helps, but in the meantime I'd really appreciate any more info that the community can provide. MTIA! :D
