I've had similar issues (but not as visually severe as this) at work, and it later turned out being the hdmi cable was poor, especially if using a displayport-hdmi adapter.
Or, it could also be faulty GPU.
I recommend testing the monitor on another computer for a while to try to figure if the problem may be the cable or monitor itself (cheapest option).
after that - if you cannot replicate the problem then second cheapest option - replace the monitor cable and see if that solve the issue.
If possible - loan a monitor+cable in known good condition. If problem still arise, then the GPU are most likely defective.
New monitor you say? This mean if you replace back to the old one, the problem goes away ?