Given the structure of the X-Trans CFA I can imagine that you're looking at demosaicing artifacts in the squarish pattern that you're seeing. X-Trans is more prone to artifacts in the demosacing process than a Bayer array, but you must understand that all demosaicing of CFAs produces artifacts -- no option exists not to do that and at 527.3% magnification no option exists not to see them. Just remember that at 527.3% magnification you may also be seeing artifacts created by the software enlarging your image to that size and/or an interaction between those artifacts and the demosaicing artifacts that you can no longer really see because of that interaction.
Look at the photo on screen at 100% magnification. Does it look OK?
