I just realize my problem has correlation with this. After reading this post i decided to monitoring my core clock and boom there you are the culprit. A lot of things are broken with amd driver apparently. The effect is not that big with 60hz but it's clearly a killer with 75hz.
Most likely AMD will try to get more fixes out the door before long. bad drivers are not in their best interest long term.
I spent a wad on a good 4K panel with the right bells and whistles. My panel supports the Windows HDR feature and it is IPS so it is real RGB not that fluff that TN panels flog.
So this puts demands on video cards far worse than these recent low res high frame rate panels. Right now I have a fossilizing RX 480 8GB and it has been a stalwart of stability. Flakey drivers notwithstanding.
Damn, what's the update? Could you fix the issue? I was going to upgrade to the same GPU for a 75Hz monitor. (That too of a LG, like yours.)