Feko: ERROR 40619: Intersecting elements found

Hi, I am having the error ERROR 40619: Intersecting elements found with my reflector when running the FEKO solver.

• I have one single 3D element created by subtraction, therefore not needing to union anything.
• The reflector is aluminum, so I set the region of the reflector to free space and added aluminum with thickness = actual thickness to all faces of the reflector.
• The meshing is done by default mesher with meshing size standard and custom growth rate = 10.
• I checked Mesh > Find > Clashing Geometry, Mesh > Find > Intersecting Triangles, etc. and all of them yields negative.
• Model Status is valid.
• The videos in this post seems to be obsolete. The POSTFEKO viewing-the-mesh technique is also not practical since my model has ~2M triangles and ~7k lines of "intersection found" messages in my .out file. 

What is the cause of this problem? Why is it not validated by Mesh > Find tools? 

P.S. My reflector: