it's a problem with projection painting. if you look closely you will see that at some edges it doesn't completely paint over them (even with bleed set to 8) and that some wrong colored pixels reach into the uv-face. this will lead to seams.

my script works but it of course it will extend those garbage pixels and produce errors there.

so you can try to fix it manually by painting the problematic areas directly in the uv-editor (probably you forgot some areas when you tried this - you always have to look at both borders of a seam) or we can make suggestions for fixing this projection painting problem at the blender forum.