Microsoft released KB4501375 for Windows 10 version 1903 recently to fix a number of issues. One of the fixed issues affected calibration loaders and applications like the popular F.Lux program that make use of the SetDeviceGammaRamp API.
Update: The June 26 update for Windows 10 version 1903 fixed the issue. according to the release notes.
The changelog confirms that Microsoft fixed the issue in KB4501375:
Addresses an issue that may cause Night light, Color Management profiles, or gamma correction to stop working after shutting down a device.
It appears, however, that Microsoft introduces a new bug that causes banding on gradients even when calibration is not active. Any program or game that loads an ICC profile may be affected by the issue.
The issue is that severe that Eizo published a support page on the company website in which it recommends to avoid PCs installed with Windows 10 version 1903 at the time.
The company notes that tones are not displayed correctly, and that the issue affects all monitors and all graphics boards.
We highly recommend not using a PC installed with Microsoft Windows 10 (1903) for the time being, especially for diagnostic imaging or graphics editing which requires tone accuracy.
Windows 10 version 1903 users may look at gradients, e.g. on this monitor test page, to find out if they are affected by the issue. The gradient should be smooth; a device is affected by the bug if stripes are noticeable when you look at the gradient.
A workaround has been published, e.g. on the DisplayCal forum, that suggests to disable the Calibration Loader task in the Windows Task Scheduler.
Note that it is required to make the change again if the associated profile is changed.
Microsoft released the final version of Windows 10 version 1903 at the end of May 2019 to the public.
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