Point cloud clipping boundary... no data visible

I've been using the polygon clipping boundary to create thin, vertical slices through an attached point cloud file (.pcg format). I am finding that the resulting slice often has large areas where the point cloud is missing. As I move the grips around, suddenly large portions disaapear. I have tried on different machines with the same result. This is of major concern as I could end up missing crucial data in the model I am working on!

Is there a system variable that could potentially affect this. I have tried various combinations of density/auto update/real time density settings.

Has anyone experienced a similar problem?

Attached photo showing problem...

Thanks

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Image may be NSFW.
Clik here to view.