I was working away on a small residential project, and suddenly my elevations with vectorial shadows went from almost instantaneous to a couple of minutes each. I finally tracked this down to the AC gutter object. It seems that if you turn the "guard" on via the checkbox, the object creates a 3D wire mesh, with every wire modeled! Needless to say, casting shadows for a bizillion surfaces, all of which are seen only inside the gutter itself, takes awhile. This is just a cautionary warning for others who have mysterious shadow slowdowns. Also a plea for object developers not to program dirty tricks like this.
Richard
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Richard Morrison, Architect-Interior Designer
AC26 (since AC6.0), Win10