I'm using 2.8.4 and have not specified a special author template. I can correctly view a list of any author's posts at the /author/[userid]/ URI *except* for the main administrator login (user ID#1) - that always 404s.
The the_author_posts_link(); methods etc all generate valid links for every user except this administrator, which gets invalid links using the display name ('/author/Firstname Surname/').
This admin user is the author of many posts, and the name is always correctly added to the user's posts - but always with the invalid link.
Even when you directly enter the URL to the "correct" author's page, ie. /author/[userid], there is a 404 error.
Is this deliberate behaviour? It's quite annoying, for the purposes of the blog!