[Landscape] Importing heightmap precisely ? (including screen shot)

I have 2 landscapes inside UE4, each with the size of 1009x1009
I also have a heightmap texture (16 bit grayscale png) in size of 2018x1009

I then opened the heightmap in GIMP, cut it in 2 exactly at 50%, and saved each part to a file.
I then imported the files each to a landscape - but some vertices have height differences!

I’m not sure where even the problem is;
Is it UE4? If so, how do I fix it?
is it the .png file format? If so, what are my alternatives?

Enable worrld composition import the two tiles,
set landscape smoothing brush to power zero and run over edges

Do not split your heightmap and use a 2017 x 1009 terrain on import of the heightmap

Paul G