Duplicate artboard bug
When you do "duplicate artboards" from the artboards window it always appears vertically aligned with the selected artboard and to right of the rightmost artboard. If there is no room it fails with "Cannot create artboard outside of the canvas" The logic for "new artboard" does not have this problem and is able to find a place for the new artboard.
Karl LaRocca commented
Top image is "Duplicate Artboard" while bottom image is "New Artboard"