Hi Roy,
Looks like your distribution exceeded the Display - Max items limit (which defines approximate maximum number of items drawn on screen) and therefore not all items are visible in the view-port. Feel free to readjust such limit (by default set to 50000) to higher values. Let me mention, that in the Forest Pack Pro/Lite 5.0.5 - "All scattering limits (Distribution-]Max.Density, Display-]Max Items/Faces) can be disabled by setting the value to zero."
Hope that helps.
Best regards,