Problem:
There is a filled region in a view, but you cannot select the region.
You see the pattern and when you turn "Detail items" on and off with Visibility Graphics the region turns on and off.
But for some reason you cannot select the region.
Cause:
The Line Style the region's boundaries are drawn in have been turned off.
Solution:
In Visibility/Graphics dialog look in the "Line" category.
Find the line style used for the boundary for the filled region (eg. "Thin Lines").
Turn it on.
If you don't know which Line Style was used, turn all of them on.
Edit the region, identify the Line Style used.
Then undo back to before you turned all the Line Styles on.
And turn the identified Line Style on.