Kubuntu 17.10: Plasma 5.12: system crash after high cpu and memory usage

I updated 2 computers to Plasma 5.12 on Kubuntu 17.10: after reboot they showed high cpu usage and high memory usage until system crash after 15 minutes or so(I guess because of running out of memory).

On another computer I updated my KDE neon developer git-stable: no problem on that one with its Plasma 5.13beta.

After googling around I found the solution:
https://bugs.kde.org/show_bug.cgi?id=368838 : plasmashell memory leak when slideshow is used for wallpaper/media frame/photo widget
https://bugs.kde.org/show_bug.cgi?id=381000 : [Regression] High CPU when background is set to slideshow : this one has been upstreamed to Qt: https://bugreports.qt.io/browse/QTBUG-62117 : endSync never called from renderloop - leads to extreme memory use

The product on kde is called "plasmashell". I don't know to what kubuntu package that belongs.

I'm using desktop slideshow on all 3 computers (rotating pictures every 10 seconds). No idea yet why on the KDE neon the bug doesn't show up as it hasn't been fixed yet.

So after changing desktop background from slideshow to single image and removing my two widgets from the desktop, my Kubuntu 17.10 computers are usable again.