On Plasma 5.12 beta, Kmail is configured to keep running in background when I close it ; but when I try to restore it (via launcher or K Menu), it kicks me back to SDDM. Akregator is configured in the same way and can be restored without any problem. testing on Archlinux with Plasma unstable repo enabled, Plasma 5.12 beta.
If it kicks you back to SDDm, the compositor died, re-assigning to KWin.
If KWin crashes we need a backtrace.
I'm on Archlinux, so I cannot provide a backtrace easily. Hopefully someone on another distro will get the same problem...
I have the same issue on Arch. I am using the wayland session and when kmail causes the crash I am thrown in a black console screen containing two lines, something about CVE resume failed and some @@@ symbols.
On an up-to-date Archlinux, I am not affected by this bug anymore.
This bug has had its resolution changed, but accidentally has been left in NEEDSINFO status. I am thus closing this bug and setting the status as RESOLVED to reflect the resolution change.