Yet another post about Revit weirdness... Struggling with setting scope boxes to multiple views via Dynamo, I noticed that some of the views returned the "null" values. I opened the view that had a "null" value, and saw that the "Scope Box" parameter was grayed out:
The reason for this weird behaviour is simple: it turned out that Scope Box parameter becomes read-only if you modify the Crop Cregion sketch. Since the Revit Scope Box is a cube, it can't be applied to those views that have non-rectangular Crop Region!
Unfortunately, there's no solution for this problem if you wish to use modified Crop Regions. If not, then select the modified crop region, press "Reset Crop":
As soon as the crop region is again rectangular, you're able to switch the Scope Box.