ssh shows no prompt and authentication fails - ssh

Question

I have a VPS running Debian 7 which I use to access through ssh for as long as 4 years.
Now, suddenly, when I try to connect to it, no prompt for password is shown, although the connection to remote sshd is open. And after a few seconds, I get the message "Authentication failed", so that I just can't login to and get a shell prompt.
Does anybody have seen this problem before? Does anybody have any hint on how I may circumvent this issue?
Thanks in advance,
Angico
Edit: I am including the full output of ssh -vvv in order to make it clearer for you to see any detail that may be escaping my attention and/or is out of my poor knowledge:
OpenSSH_7.4p1 Debian-10+deb9u3, OpenSSL 1.0.2l 25 May 2017
debug1: Reading configuration data /home/xyz/.ssh/config
debug1: /home/xyz/.ssh/config line 1: Applying options for xyz.net
debug3: kex names ok: [diffie-hellman-group1-sha1]
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *
debug2: resolving "xyz.net" port 22
debug2: ssh_connect_direct: needpriv 0
debug1: Connecting to xyz.net [12.34.56.78] port 22.
debug1: Connection established.
debug1: key_load_public: No such file or directory
debug1: identity file /dev/null type -1
debug1: key_load_public: No such file or directory
debug1: identity file /dev/null-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_7.4p1 Debian-10+deb9u3
debug1: Remote protocol version 2.0, remote software version OpenSSH_6.0p1 Debian-4+deb7u4
debug1: match: OpenSSH_6.0p1 Debian-4+deb7u4 pat OpenSSH* compat 0x04000000
debug2: fd 3 setting O_NONBLOCK
debug1: Authenticating to xyz.net:22 as 'xyz'
debug3: put_host_port: [xyz.net]:22
debug3: hostkeys_foreach: reading file "/home/xyz/.ssh/known_hosts"
debug3: record_hostkey: found key type RSA in file /home/xyz/.ssh/known_hosts:1
debug3: load_hostkeys: loaded 1 keys from [xyz.net]:22
debug3: order_hostkeyalgs: prefer hostkeyalgs: ssh-rsa-cert-v01#openssh.com,rsa-sha2-512,rsa-sha2-256,ssh-rsa
debug3: send packet: type 20
debug1: SSH2_MSG_KEXINIT sent
debug3: receive packet: type 20
debug1: SSH2_MSG_KEXINIT received
debug2: local client KEXINIT proposal
debug2: KEX algorithms: curve25519-sha256,curve25519-sha256#libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha256,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1,ext-info-c
debug2: host key algorithms: ssh-rsa-cert-v01#openssh.com,rsa-sha2-512,rsa-sha2-256,ssh-rsa,ecdsa-sha2-nistp256-cert-v01#openssh.com,ecdsa-sha2-nistp384-cert-v01#openssh.com,ecdsa-sha2-nistp521-cert-v01#openssh.com,ssh-ed25519-cert-v01#openssh.com,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,ssh-ed25519
debug2: ciphers ctos: chacha20-poly1305#openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm#openssh.com,aes256-gcm#openssh.com,aes128-cbc,aes192-cbc,aes256-cbc
debug2: ciphers stoc: chacha20-poly1305#openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm#openssh.com,aes256-gcm#openssh.com,aes128-cbc,aes192-cbc,aes256-cbc
debug2: MACs ctos: umac-64-etm#openssh.com,umac-128-etm#openssh.com,hmac-sha2-256-etm#openssh.com,hmac-sha2-512-etm#openssh.com,hmac-sha1-etm#openssh.com,umac-64#openssh.com,umac-128#openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: MACs stoc: umac-64-etm#openssh.com,umac-128-etm#openssh.com,hmac-sha2-256-etm#openssh.com,hmac-sha2-512-etm#openssh.com,hmac-sha1-etm#openssh.com,umac-64#openssh.com,umac-128#openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: compression ctos: none,zlib#openssh.com,zlib
debug2: compression stoc: none,zlib#openssh.com,zlib
debug2: languages ctos:
debug2: languages stoc:
debug2: first_kex_follows 0
debug2: reserved 0
debug2: peer server KEXINIT proposal
debug2: KEX algorithms: ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1
debug2: host key algorithms: ssh-rsa,ssh-dss
debug2: ciphers ctos: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,rijndael-cbc#lysator.liu.se
debug2: ciphers stoc: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,rijndael-cbc#lysator.liu.se
debug2: MACs ctos: hmac-md5,hmac-sha1,umac-64#openssh.com,hmac-sha2-256,hmac-sha2-256-96,hmac-sha2-512,hmac-sha2-512-96,hmac-ripemd160,hmac-ripemd160#openssh.com,hmac-sha1-96,hmac-md5-96
debug2: MACs stoc: hmac-md5,hmac-sha1,umac-64#openssh.com,hmac-sha2-256,hmac-sha2-256-96,hmac-sha2-512,hmac-sha2-512-96,hmac-ripemd160,hmac-ripemd160#openssh.com,hmac-sha1-96,hmac-md5-96
debug2: compression ctos: none,zlib#openssh.com
debug2: compression stoc: none,zlib#openssh.com
debug2: languages ctos:
debug2: languages stoc:
debug2: first_kex_follows 0
debug2: reserved 0
debug1: kex: algorithm: ecdh-sha2-nistp256
debug1: kex: host key algorithm: ssh-rsa
debug1: kex: server->client cipher: aes128-ctr MAC: umac-64#openssh.com compression: none
debug1: kex: client->server cipher: aes128-ctr MAC: umac-64#openssh.com compression: none
debug3: send packet: type 30
debug1: sending SSH2_MSG_KEX_ECDH_INIT
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug3: receive packet: type 31
debug1: Server host key: ssh-rsa SHA256:abcdefghugklmnop+qrstuvwxyzabcdefghi+jklmnop
debug3: put_host_port: [12.34.56.78]:22
debug3: put_host_port: [xyz.net]:22
debug3: hostkeys_foreach: reading file "/home/xyz/.ssh/known_hosts"
debug3: record_hostkey: found key type RSA in file /home/xyz/.ssh/known_hosts:1
debug3: load_hostkeys: loaded 1 keys from [xyz.net]:22
debug3: hostkeys_foreach: reading file "/home/xyz/.ssh/known_hosts"
debug3: record_hostkey: found key type RSA in file /home/xyz/.ssh/known_hosts:2
debug3: load_hostkeys: loaded 1 keys from [12.34.56.78]:22
debug1: Host '[xyz.net]:22' is known and matches the RSA host key.
debug1: Found key in /home/xyz/.ssh/known_hosts:1
debug3: send packet: type 21
debug2: set_newkeys: mode 1
debug1: rekey after 4294967296 blocks
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug3: receive packet: type 21
debug1: SSH2_MSG_NEWKEYS received
debug2: set_newkeys: mode 0
debug1: rekey after 4294967296 blocks
debug2: key: /dev/null ((nil)), explicit
debug3: send packet: type 5
debug3: receive packet: type 6
debug2: service_accept: ssh-userauth
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug3: send packet: type 50
And here, after some time...
Authentication failed.

Answer 1

Your ssh client is trying to use an already defined connection. Do you have any ssh connection configured in .ssh/config? Does it match the connection you want to use?
Also, do you have defined any public or private key in the folder .ssh? if you have some keys there, the ssh clien will try to attempt to use it for connecting and after some tries, will fail. If it is the case, as described here you can use:
ssh -o PreferredAuthentications=password -o PubkeyAuthentication=no example.com
to skip the use of any existing key.