Just in case you haven’t heard about this potential root cause: https://superuser.com/questions/1406140/monitor-screen-that-blanks-due-to-static-electricity-in-my-chair
Debian operating system
Debian is a free operating system (OS) for your computer. An operating system is the set of basic programs and utilities that make your computer run. Debian provides more than a pure OS: it comes with over 59000 packages, precompiled software bundled up in a nice format for easy installation on your machine.
Thanks for your input, I am not getting up though. In this last instance, I had just closed LibreOffice after editing a document.
Here is a clue perhaps from Journalctl:
Aug 11 17:25:17 adam plasmashell[14949]: This plugin supports grabbing the mouse only for popup windows
Aug 11 17:25:18 adam plasmashell[14949]: This plugin supports grabbing the mouse only for popup windows
Aug 11 17:25:18 adam plasmashell[14949]: QWaylandShmBuffer: mmap failed (Invalid argument)
Aug 11 17:25:18 adam plasmashell[14949]: QWaylandShmBuffer: mmap failed (Invalid argument)
Aug 11 17:25:19 adam plasmashell[14949]: QWaylandShmBuffer: mmap failed (Invalid argument)
Aug 11 17:25:23 adam kwin_wayland_wrapper[2483]: error in client communication (pid 12396)
Aug 11 17:25:23 adam plasmashell[12396]: wl_display@1: error 0: invalid object 213
Aug 11 17:25:23 adam plasmashell[12396]: The Wayland connection experienced a fatal error: Invalid argum>
Aug 11 17:25:23 adam plasmashell[12396]: The Wayland connection experienced a fatal error: Invalid argum>
Aug 11 17:25:23 adam systemd[2384]: plasma-plasmashell.service: Main process exited, code=exited, status>
Aug 11 17:25:23 adam systemd[2384]: plasma-plasmashell.service: Failed with result 'exit-code'.
Aug 11 17:25:23 adam systemd[2384]: plasma-plasmashell.service: Consumed 1min 59.306s CPU time.
Aug 11 17:25:24 adam systemd[2384]: plasma-plasmashell.service: Scheduled restart job, restart counter i>
Aug 11 17:25:24 adam systemd[2384]: Stopped plasma-plasmashell.service - KDE Plasma Workspace.
Aug 11 17:25:24 adam systemd[2384]: plasma-plasmashell.service: Consumed 1min 59.306s CPU time.
Aug 11 17:25:24 adam systemd[2384]: Starting plasma-plasmashell.service - KDE Plasma Workspace...
lines 907-931/975 94%
> Aug 11 17:25:23 adam kwin_wayland_wrapper[2483]: error in client communication (pid 12396)
> Aug 11 17:25:23 adam plasmashell[12396]: wl_display@1: error 0: invalid object 213
> Aug 11 17:25:23 adam plasmashell[12396]: The Wayland connection experienced a fatal error: Invalid argum>
> Aug 11 17:25:23 adam plasmashell[12396]: The Wayland connection experienced a fatal error: Invalid argum>
> Aug 11 17:25:23 adam systemd[2384]: plasma-plasmashell.service: Main process exited, code=exited, status>
> Aug 11 17:25:23 adam systemd[2384]: plasma-plasmashell.service: Failed with result 'exit-code'.
KDE's crashing and getting started back up. Due to how Wayland works this will also take down most programs you were running.
Why is KDE crashing? No idea. You may have better luck with Xorg if you aren't reliant on any Wayland niceties (proper multiple monitor support, for example)
edit: https://bugs.kde.org/show_bug.cgi?id=447717 looks like a candidate, but there isn't enough detail to make sure
I have rebooted into X11, we will see if there are any more instances.
This can also happen if your GPU isn't getting enough power. Try unplugging some components to test if the reduction in power draw helps or swapping your PSU out for one with a higher wattage.
I am not sure I can do that with a laptop.
Oh, haha I seem to have only skimmed your post and missed that point.
I can't tell you why but it seems like plasma crashed (-> screen black and all opened programs gone) and restarted (-> came back). That's what I can tell from your description. In your logs you can look for errors from plasma, kwin and maybe something with the gpu driver.