I've found a better way to deal with the unmiminising crashing with Kwin. In System Settings > Desktop Effects > Advanced there is a settng for "Keep window thumbnails". If you change that to "Always (Breaks minimization)" then it cures the crashing. It still allows minimistation, but (from a bit of googling) it just handles the minimisation differently. Sorted!
I've found a better way to deal with the unmiminising crashing with Kwin. In System Settings > Desktop Effects > Advanced there is a settng for "Keep window thumbnails". If you change that to "Always (Breaks minimization)" then it cures the crashing. It still allows minimistation, but (from a bit of googling) it just handles the minimisation differently. Sorted!