ssh – sshd never accepts public key offer

I have used PublicKey logins on a number of my servers for months without trouble. I generated the keys on my client machine and copied to the server’s ~/.ssh/authorized_keys using ssh-copy-id. All well and good until one machine stopped accepting key-based logins the other day. Obviously there has been a change, but the sshd_config is the same as it was and as the other server.

Running the connection verbosely offers the following:

debug1: Authentications that can continue: publickey,password
debug3: start over, passed a different list publickey,password
debug3: preferred gssapi-with-mic,publickey,keyboard-interactive,password
debug3: authmethod_lookup publickey
debug3: remaining preferred: keyboard-interactive,password
debug3: authmethod_is_enabled publickey
debug1: Next authentication method: publickey
debug1: Offering public key: /home/kapn/.ssh/id_rsa RSA SHA256: <deleted for post>
debug3: send packet: type 50
debug2: we sent a publickey packet, wait for reply
debug3: receive packet: type 51
debug1: Authentications that can continue: publickey,password
debug1: Trying private key: /home/kapn/.ssh/id_dsa 
<and so on until it asks for a password>

My sshd_config file

Port 2201
PermitRootLogin without-password
PubkeyAuthentication yes
ChallengeResponseAuthentication no
UsePAM yes
TCPKeepAlive yes
# All else is at default settings.
# With the exception of the Port, PubKeyAuthentication and PermitRootLogin settings, 
# I didn't intentionally change anything here.

Any thoughts on where to look for trouble? Is there data to be gathered other than via the -vv switch on ssh?