As the original tif file for displacement has around 100mb, I loaded it into Affinity Photo and exported it again as a 16bit tiff. (only 5mb now)
I rendered again with C4D standard renderer and look, something similar to what I get with Corona. Edges clearly visible. See image a
So I exported it again as a 16bit png and the edges disappeared. Note that the png has a linear color profile and the tiff has not. (I don't understand why...) See image b
Image c to compare. Edges are visible in both cases.
Could it also be a color profile issue? If someone has a hint, I would be very glad :)