That's your typical high refresh rate TN panel experience, with terrible pixel inversion artifacts, because that's how we call what you see. From my experiences, this phenomenon is fairly common in high refresh rate TN panels. I have previously seen a complaint about Omen X 25f inversion artifacts issue, and I experienced it myself, as you can read
in here.
Actually, the very first high refresh rate TN monitor that does not suffer from pronounced pixel inversion artifacts for me is the newest BenQ Zowie XL2546K, surely the best TN monitor I tested so far.
I advice you return your Omen X 25f and either try your luck with another unit, or choose something else entirely. You do not necessarily have to rely on TN panels for good gaming performance anymore, new-gen 240 Hz IPS (and 360 Hz IPS) panels are really good options these days as well, and they offer better overall viewing experience with better colour performance and wide viewing angles. There are plenty of discussions about these monitors around here!