In my logs, I find the following:

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nov 20 23:36:07 sysoppad sddm[509]: Display server stopped.
nov 20 23:36:07 sysoppad sddm[509]: Running display stop script  "/usr/share/sddm/scripts/Xstop"
nov 20 23:36:07 sysoppad sddm[509]: Removing display ":0" ...
nov 20 23:36:07 sysoppad sddm[509]: Adding new display on vt 1 ...
nov 20 23:36:07 sysoppad sddm[509]: Display server starting...
nov 20 23:36:07 sysoppad sddm[509]: Running: /usr/bin/X -nolisten tcp -auth /var/run/sddm/{aa56798b-7ee2-4843-9309-db5daf5614d8} -background none -noreset -displayfd 19 vt1
...
nov 20 23:36:07 sysoppad kded5[7476]: The X11 connection broke: I/O error (code 1)
nov 20 23:36:07 sysoppad sddm[509]: Running display setup script  "/usr/share/sddm/scripts/Xsetup"
nov 20 23:36:07 sysoppad sddm[509]: Display server started.
nov 20 23:36:07 sysoppad sddm[509]: Socket server starting...
nov 20 23:36:07 sysoppad sddm[509]: Socket server started.
nov 20 23:36:07 sysoppad sddm[509]: Greeter starting...
nov 20 23:36:07 sysoppad sddm[509]: Adding cookie to "/var/run/sddm/{aa56798b-7ee2-4843-9309-db5daf5614d8}"
nov 20 23:36:07 sysoppad sddm[509]: Signal received: SIGTERM
nov 20 23:36:07 sysoppad sddm[509]: Socket server stopping...
nov 20 23:36:07 sysoppad sddm[509]: Socket server stopped.
nov 20 23:36:07 sysoppad sddm[509]: Display server stopping...
nov 20 23:36:07 sysoppad sddm-helper[16560]: [PAM] Starting...
nov 20 23:36:07 sysoppad sddm-helper[16560]: [PAM] Authenticating...
nov 20 23:36:07 sysoppad sddm-helper[16560]: [PAM] returning.
nov 20 23:36:07 sysoppad sddm[509]: Display server stopped.
nov 20 23:36:07 sysoppad sddm[509]: Running display stop script  "/usr/share/sddm/scripts/Xstop"
nov 20 23:36:07 sysoppad sddm[509]: QProcess: Destroyed while process ("/usr/libexec/sddm-helper") is still running.
nov 20 23:36:07 sysoppad systemd[1]: Stopped Simple Desktop Display Manager.
...
nov 20 23:36:08 sysoppad kded5[16602]: QXcbConnection: Could not connect to display :0
nov 20 23:36:08 sysoppad drkonqi[16603]: QXcbConnection: Could not connect to display :0

The last two lines here are at the ‘alert’ level.
This is repeated for every shutdown. Because it is upon shutdown, there aren't any direct practical consequences.

However, I'm having issues that almost always on resume from suspend/hibernate my X11/KWin screen is black (mouse pointer visible, movable). I was wondering that perhaps the above error points to some configuration problem that may also be responsible for this black screen problem and so therefore I want to fix this.