If you use the grouping tool to select polygons I found there are 2 possible reasons why you cannot select them: Either you are too close to the polygons and you have to move the camera back to pick them.
The other reason is that these are backfacing polygons. If you select "reverse group normals" you can now pick them and afterwards you deselect the reverse group normals to restore the grouping.

For the rest I do not have problems with the grouping tool and use it quite often