I started Plasma (Wayland) from SDDM but when I logged out, I did not get back to SDDM but to VT showing only ^@ and not accepting input (not even switching to other VTs). Reproducible: Didn't try
Looks like SDDM issue - https://github.com/sddm/sddm/issues/897
*** This bug has been marked as a duplicate of bug 372789 ***