I was messing with the sticky notes widget the other day. I wanted to see how many can I add to the panel, so I spam clicked it 5 times and it froze the entire plasmashell.
I had to manually edit the plasma config file to remove them or else plasmashell just never worked.
After fixing plasmashell, I tried to add 1 sticky note again, and plasmashell froze again. So I just never touched it ever after.