Why is plasmashell using 100% cpu?

Solution 1:

I'm having a similar issue. The CPU usage increases over time and never goes back down. There is definitely an issue with plasmashell. The only way to deal with the issue is to run:

killall plasmashell; kstart plasmashell; exit

This will kill, restart plasmashell then exit the shell. If you don't exit the shell it will fill up with output from plasmashell.

Solution 2:

Plasmashell has had a bug for a long time that any kind of animation in the task bar causes it to use 100% CPU, such as when copying a file, connecting to a Wifi, and even the CPU monitor (that seems to be fixed now).

It seems like the bug is reported here and will be fixed in Plasma 5.8.6.