KDE high cpu usage when screen locked

I’m on the latest Leap 42.3 fully updated. I’ve just noticed that when the screen is locked the process kwin_x11, plasmashell and kscreenlocker have an higher cpu usage, 6%, 2% and 2% respectively. While the screen is unlocked they are at less then 1% (without user interaction).

I already disabled slideshow wallpaper and i’m using a plain color background and screen lock.

I found a lot of thread on several forums speaking about abnormal kde cpu usage, but nothing seem applying to this case. What can I try? Any similar experience?

Thank you all.