I think you need to change the value of id in select field
$output = "<select name="attachments[{$id}][kgal_artwork_artist]" id='attachments-'.$id.'-kgal_artwork_artist'>";
I think you need to change the value of id in select field
$output = "<select name="attachments[{$id}][kgal_artwork_artist]" id='attachments-'.$id.'-kgal_artwork_artist'>";