MAYA _ can't do planar mapping uv / OBJ group problem

Sometimes, there is some buggy mesh on which Maya can't apply a planar mapping and when trying to export and import obj to clean the mesh we get this warning :

"Your OBJ file contains faces shared by multiple groups. Maya cannot create multiple objects for this file. A single mesh object will be created instead. The OBJ group information will be captured in Maya sets."

Here is a trick (for multiple objects) :

export to OBJ turning groups and point groups option off then import it in Maya then mesh > separate.