Recently I have come across a post regarding color differences between layered and exported files here https://community.adobe.com/t5/photoshop/problem-with-curvers/m-p/11036512?page=1 but it turned out, once again, to apparently be about the preview of Adjustment Layers on noisy images at magnifications other than View > 100%.
I seem to recall that setting the Cache Levels to 1 could be used to address this issue (at a cost naturally). And according to this page https://helpx.adobe.com/photoshop/kb/optimize-photoshop-cc-performance.html it should be possible, but when I set the Cache Levels to 1 they revert to 2 at restarting Photoshop. (Photoshop 21.1.1 on macOS 10.15.3)
I had access to an old computer that still has Photoshop CS2 installed and there it is possible to set Cache Levels to 1.
So either there was a decision to abandon it (without amending the Reference) or somewhere between CS2 and CC 2017 it may have been accidentally invalidated.
It’s not something that affects my daily work at all but for the aforementioned special circumstance (when Adjustment Layers preview on particular content differs noticeably with different magnifications) it was a »solution« that seems to be missing now.
Wanted to see if the report was carried over from feedback.photoshop.com and there it is!
Alas, the bug also seems to continue being with us.
Lately it seems like the »Adjustments or Layers Styles disappear on saving flattened copy«-kind of reports pop up about weekly or so, so I hope this might be addressed in the future.