When reference_image names are automatically normalised so is the reference_folder which should not be the case.
On Windows this is not a problem as Windows ignores case in paths anyway, It however causes the test case to fail on MacOS and Linux (and probably any other *nix)
https://eficode.github.io/robotframework-imagehorizonlibrary/doc/ImageHorizonLibrary.html#Reference%20image%20names