Can you share the processing options you have used for the 3D Textured Mesh? Maybe 3DS Max does not handle high resolution settings and tries to downsample the mesh.
I found this similar post about this issue, but there is no solution so far. Hope that someone more experienced with 3DS max can help out here.
EDIT: Maybe try changing the illumination of your model in 3DS Max as described here: How to import Pix4D outputs to Autodesk