sshd ignores authorized_keys and keeps trying authorized_keys2

It looks like it's falling back to authorized_keys2 for compatibility reasons when it fails to find a valid authorized_keys file. Check that your authorized_keys file is correctly formed.

Can the user with uid=1000 access the .ssh/authorized_keys directory? What OS are you running? Some distributions with SELinux enabled can disallow sshd to read from .ssh/authorized_keys. You can restore that using: restorecon -R -V /home/xxx/.ssh/

I had the exact same issue with the same message in the error log. However, it was due to a wrong username used when connecting to a server.

In other words, I was typing: ssh -i ~/.ssh/id_key myuser@IP_Address while the authorized_keys file was located in /root/.ssh folder. After changing the login command to ssh -i ~/.ssh/id_key root@IP_Address everything started working fine.