I have this fairly simple shapes and OffsetSrf doesn’t work properly as probably with many more complex shapes.
If this is not a bug, the command is unreliable and therefore useless in many cases. Maybe there is a solution to lower precision that it will work in these cases. Maybe recalculating surfaces in the command?
I know Fusion and Solidworks have also their problems with certain intersecting surfaces and angles but @martinsiegrist did it in Grasshopper with very good results and stable processing and recalculation of shapes that it would work.