OK. Now I have done some testing myself, and can confirm that displacement on large scale is problematic with Corona.
My test was designed to see how far away you can see displacement sized around 20-25 cm, and in both 4k and 6k renderings I could still see it at 1km distance, even with the denoiser on (Corona). Pictures attached.
But at 8k the problems begin. There is lots of artifacts in the render, and Corona gives a warning about low RAM (I only got 64Gb). Low RAM however should only cause a slow render, and NOT give artifacts.
I have tried to locate the problem, and one thing I noticed is, that when the "Primitives displac." number goes higher than 1.000 M I start to have artifacts.
Hope it helps.