The lack of continued info on this "fix" over the years since it was first posted seems odd. If it wasn't for me stumbling onto the text, I would have never found it in a web search. Same is true with the -03 version of the adapter. I did find some on that but not as much as one would expect. Although, I know some people say they do not see the lines. They're very obvious to me, much like your photo.
The inclusion of "AGA" banding in the instructions is somewhat inaccurate as it affects ECS Amigas also. I think that came about only because people started to use the adapter with their AGA Amigas since they could directly connect their VGA multiscan monitors and use the new screenmodes.
I verified you have pin 15 on your adapter. Maybe the choice of ground is not the best?
I was thinking about just using one of the solder points for the screw mounts. That's a ground I'm sure.