Not spawning areas?

I have a blueprint as shown below

http://puu.sh/tmGRn/8380388df8.png

This generates the below distribution of items

http://puu.sh/tmGMn/8449b0c339.jpg

however I have those big spaces that are clearly available to spawn in but nothing will spawn there??? Its not collision eaither as you can see there is nothing blocking…

http://puu.sh/tmH5e/027d07b5a4.jpg