… and that there won’t be any programs accessing said cache when logged out of the GUI.. 
That was the implication, yes.
The right place would be bugs.kde.org. You will need to sign up for an account first, and you may also want to check whether the bug was already reported before you file yet another bug report against kwin.
Chances are that it was indeed already reported, given that kwin is a core component of the Plasma desktop environment, and that the KDE developers will thus be paying much attention to anything causing kwin to crash.
Does the issue with the panel disappearing occur when you don’t have a compute task running?
This is a different issue to the one you reported. But it is potentially related to changes you made to your system at that time.
Additionally, you are now using Wayland not X so the changes in that thread will not work.
KDE / Plasma had a bug reporting facility once, it’s not the case any longer?
No, no, I mean inside the apps. But I might remember wrongly
Sometimes they were in the about sections(or was that kde?). I wonder if I might have to look again at the last iteration of plasma. In my personal opinion in gnome all parts are better integrated but then again, I haven’t used plasma in a long long time
Sadly it still appears.
But there still was an X11 process in nvidia-smi sot that made me think it was used by kwin
However, now that I have updated to Plasma Login Manager, it is gone, so it was coming from SDDM
I’ll see how I can report this in the KDE system, thanks for your patience.
PS: Sorry for not responding earlier, I missed your question in the cascade of emails
One more thing I just thought of for the overall picture. In Firefox what do you have under about:support - “Graphics/Window Protocol”?