NVIDIA driver bug? Inaccurate HDR output after waking PC from sleep

[dogelition]

I noticed some very strange behavior with HDR output on my Windows 10 install with an RTX 4070 (going back several months of OS updates and driver versions) that I cannot reproduce on a newer Windows 11 install on the same PC. After waking my PC from sleep, any VCGT-related operations cause the screen to take on a slight green tint that seems impossible to get rid of except by switching into SDR and then HDR again.

I can reproduce it consistently with these steps:

1. With HDR disabled, ensure no applications that could modify the VCGT are running (e.g. DisplayCAL Profile Loader)
2. Put the PC in sleep and wake it again
3. Enable Windows HDR
4. Change pretty much anything in Windows’s Color Management settings panel, e.g. assign a different ICC profile for SDR (which should not affect anything in theory, due to HDR being active). As soon as this happens, the entire screen takes on a slight green tint.
5. Optional: Repeatedly reproduce the issue by switching into SDR, then HDR again, and clicking “Set as Default Profile” on the SDR profile.

This happens even with NVIDIA’s “Override to reference mode” setting enabled, which should prevent any VCGT changes and ensure unity output. The tint also doesn’t show up on any HDR screenshots or screen captures, which makes me fairly confident that this is actually a GPU driver issue.

I also came up with a much more visually clear way of testing for this issue, but it requires reference mode to be disabled:

1. After a reboot, enable Windows HDR and load the attached .cal file via DisplayCAL or the dispwin command, which should give everything except peak white a strong green tint.
2. Look at a 100% peak white HDR patch, e.g. on the “PQ/ST 2084 levels in nits” page of the DisplayHDR Test app. This should appear perfectly white.
3. Put the PC in sleep and wake it again. Now, the patch appears green.

I reported this issue to NVIDIA via their Display Driver Feedback Form, but I have little hope of them investigating this if it’s just a single report of a rather subtle and niche issue. Can anyone else reproduce this at all?

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