If I remember correctly I think I found fast start did correct the problem on what was then build 19H1 which I think would be the forerunner of your 1903 build.
I haven't tried disabling fast start on this clean install of build 20H1 (18875) which is the latest 'skip ahead' build.
duplicate removed
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ctrl+shft+win+b does not fix confirmed
As a test (today) I have first tried the night light when running on battery and find it seemed to be able to be enabled/disabled correctly.
I've now turned off Fast Start and again find it enables correctly. Whether it will do so automatically at the correct time remains to be seen.
Nightlight kicked in automatically at the alloted local time. So yes, it seems disabling fast start has fixed it it for me, at least on this occasion. I did keep trying to manually turn it on and off as well and that also worked OK.
I wish we knew exactly what was causing it. There's some talk of it being a registry bug where the keys corresponding to Night Light settings are absent. However, as a test I manually created these keys in the registry but this did nothing to fix the issue which is what has me confused.
I think if it were that simple MS would have issued a definitive fix ages ago. Are Intel graphics a common factor I wonder.
- We’re investigating reports that on certain devices if fast startup is enabled night light doesn’t turn on until after a restart. (Note: The problem will occur on a “cold” reboot or power off / power on. To work around if night light doesn’t turn on, use Start > Power > Restart.)
Announcing Windows 10 Insider Preview Build 18885
I'm glad they're aware of the bug. I wonder if a quickfix cab or kb update could be issued in the meantime to workaround while we wait.
I have the same problem on my PC. Win 10 version 18362.86 ;/
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