ZBrush UVmaps problem

ZBrush UVmaps problem
We have a 3D model in ZBrush and we extract the UV map from it. Exporting it in SubstancePainter and trying to set the textures however , leaves white spots in some places. I have seen that depending on the size of the UV Map the white spots appear in different areas. What could the reason for this behaviour be? Computer Graphic Perspective , what is the reason for this problem and what would be a good idea to overtake , in order to fix it ?
ZBrush UVmaps problem