I’ve eventually got around to firing up a Win 10 laptop to look into this, with some interesting results.
I let it do all the pending Windows (and other) Updates and then opened CCleaner FREE v6.33.
NOTE that the testing below is all happening with CCleaner Free v6.33, which rules out it being something that was changed with CCleaner v6.34.
Some seconds after opening CCleaner v6.33 all of my desktop icons refreshed (went blank and then came back).
That had not happened before, now it seems to be happening more often than not when I open CCleaner 6.33 on that Win 10 machine. (The time between opening CCleaner and the Desktop icon refresh varies, which seems odd).
However that isn’t what was being described here so I carried on testing.
Next I tried a right-click clean of just one option in Custom Clean (I did the Edge Chromium ‘Session’).
That ran and then after about 5 seconds the CCleaner UI flashed grey, exactly as has been reported - BUT THEN I was shown this ‘get an upgrade’ nag screen:
Further cleans, even a full ‘Run Cleaner’, resulted in a quick greying ‘flash’ about 5 seconds after each clean, but the nag screen was not shown again.
Even after closing CCleaner and re-opening it there was no nag, - The nag will be on a 'once shown don’t show again for so many days’ timer which is why you only see it the one time.
This odd behaviour may well be due to a Windows graphics update, but I’m not so certain that it’s Intel
I can see this issue on my Win10 laptop, which has Nvidia graphics. (Quadra NVS 130M).
It is not happening on my Win 11 laptop, which has Intel graphics. (UHD Graphics).
EDIT 1 -
As the grey flash-screen appears to be associated with that nag screen I tried a further test - I registered that v6.33 as Pro rather than Free.
As I suspected would happen that stops the flashing happening, because there is no reason to show you that ‘upgrade’ nag screen if your CCleaner is already Pro.
Reverting it back to Free and the grey flash-screen after running any a clean starts again.
(However I wouldn’t be surprised if some other pop-up screens in Pro might also trigger it).
EDIT 2 -
It doesn’t happen with Health Check (or at least I can’t make it happen with Health Check).
I believe that HC uses a different, more modern graphics programming and commands than Custom Clean does, I seem to recall some previous display issues happening because of that difference.
BTW. I have now updated the CCleaner on my Win 10 machine to v6.34 Free.
It is still showing the grey flash-screens after a clean. (If I upgrade it to Pro they stop).