Tearing on secondary display when cloning displays

[GoldenOne]

So I've been trying to sort this for a while now.

I have two displays, an acer x34P and an elgato 4k60 pro capture card.
the x34p connected via displayport and the 4k60 pro via hdmi 2.0. (I have a dual-PC setup and am not using passthrough)

When I "Clone" the displays, the display that is set to be the "clone source" looks perfect. But the cloned display has a stationary tear as shown here: https://clips.twitch.tv/AwkwardDelightfulPeanutYouDontSay

This occurs regardless of resolution or framerate.

I have my capture card and monitor both set to a resolution of 2960x1440 @120hz (the capture card supports this resolution, no scaling etc involved) and even though both are the same res, same refresh rate the tearing still occurs.
I thought it was a capture card issue, but as mentioned, setting the capture card as the "source" display means it starts working perfectly, and the monitor starts tearing.

-Gsync is disabled
-Timings are EXACTLY 120.000hz vertical and 180.000khz horizontal on both displays.


Is this just a driver issue? Is there any way at all to fix it? Something I can change in my capture card's EDID or in nvidia profile inspector etc?
I am on the latest drivers

It seems others have had a similar problem to me: