I’ve experienced a couple of crashes when dragging a window to the top of the screen in KDE Plasma. The system totally freezes and doesn’t seem to respond to anything - a hard reset is the only way out.
Looks like this is a KDE bug (500757 – Dragging a Window at Top of Screen causes Hard Freeze) with a fix merged and waiting for release (481610 – Dragging a window along the top screen edge makes it follow the mouse by 1 pixel increments).