I found by using this permalink structure
/%category%/%author%/%postname%/%post_id%
urls like: /catname/authorname
will return archive pages that are sorted correctly.. as in it will show all posts matching catname and authorname.. you change the authorname it re-sorts and shows posts matching new authorname, but when you add /feed/ it 404’s
/catname/authorname/feed/ = 404
I thought any page can be requested as rss?
Thoughts?