When I go to save an artboard (save or export) that I have used a transparent to black gradient in, it completely messes up the image and goes crazy with the effect. Here are the images of what I save vs what I see in Photoshop:
This seems like a bug.
The second artboard in the image is very similar but does not have the same problem despite having layers copied from one to the other just moved around and resized a bit. (One that looks fine is bigger image.)