Are you trying nightly builds? Or some suspicious distri (Like KDE Neon)?

KDE is rock stable in my experience. Runs for weeks or sometimes even month (between kernel update reboots) without any crash or this like.

I'm running Debian Testing. So it's usually not the newest release of the desktop. I guess this makes it so rock solid for me.

Anecdotical story regarding stability of a DE: I had to use Windows 10 lately. I think the compositor crashes quite often if one has to may open windows. :-D