Why does turning off Auto Smooth removes blotches? Often with imported OBJ meshes I noticed that some seemingly random vertices are surrounded in dark blotches and sometimes adjacent ones are pale. Yet all the readable characteristics are identical to a normal vert angle stats. So why when I was messing around I unchecked Auto Smooth did theses anomalies go away?
I sometimes had effects like this because custom split normals data was imported and got distorted somehow. AutoSmooth only seems to work reliably if this data is deleted, try the button in the Mesh Data section to clear custom split normals data: