I discovered that because my WP system has thousands of users, and only a few dozen authors, the author pages would stop working.
I would see a blank page and no errors would come up. This effect happened on three different servers and I determined the problem was with the number of users the list_authors function would search through to find authors. The DB server was timing out on the query.
My quick solution is to edit the query in that function to include WHERE ID < 75 and keeping all my subscribers with an ID > 500. I also edited the admin exclusion to read AND user_login <> 'admin'.