Hi there,
Just as a sanity check I put together my own small project to test VSync both in the editor and in a build in 5.4, and as with your sample projects, I cannot reproduce this issue.
It does seem to be project dependent, so we can rule out any NVIDIA Control Panel (or equivalent) settings.
Does your project use any platform specific plugins, such as Intel’s XeSS plugin? (or more generally, any plugins with a rendering focus at all?)
If you would be able to attach your project’s DefaultEngine.ini, that would also be helpful to review.
Thanks,
Hayden