I've had issues in the past with using IndieAuth logins and Known. Sometimes it's finicky and prefers the http://sitename.com/profile/username pattern and won't work with http://sitename.com.

I'll note that I've tried logging in with both:
http://stream.boffosocko.com/profile/chrisaldrich
http://stream.boffosocko.com
and didn't have any problems/issues.
I suspect that for multi-user installations, Known needs the /profile/username addition to distinguish which account to allow publishing to. If I recall OwnYourGram had issues like this in the past if you need advice on what the solution was.

Does Kevin have a multiuser installation? Perhaps he was trying to log in with one account while logged into another?