Stutter when used on a G-SYNC display

When a G-SYNC display is used we have 3 different scenarios:

• Compositor OFF -> both cursor and window move smoothly at high refresh rates.
• Compositor ON (glx) -> cursor stutters, windows move smoothly.
• Compositor ON (xpresent) -> cursor moves smoothly, windows stutter.

Observations:

• Version: git from 3 weeks ago (i.e. 4.16.1).
• On 4.14.6 the issue is also present.
• On 4.12.5 G-SYNC doesn't work, therefore it has none of the issues I'm reporting here.
• This is noticeable even at 60 Hz, but at 85 Hz or higher is more evident.
• The moment I disable G-SYNC all scenarios behave perfectly.

This was somehow discussed here, but I couldn't find any gitlab issue related to it. The solution he found was disabling compositor, which, of course, is not reasonable.