SSH se kousne pri prihlasovani (timeout, bad protocol version)

Mam tri pocitace - kumbal, notas a prcek. Z kumbalu a notasu se pripojuji na prcka pres ssh. vsechny tri jsou na lokalni siti, k prihlasovani slouzi verejny klic, na vsech pocitacich stejny. Na vsech pocitacich je tataz verze SSH z Debianu testing. Nekolik mesicu vse fungovalo a dnes najednou ne. Z notasu se nadale bez problemu prihlasim, z kumbalu ne. Situace vypada nasledovne:

ondra@kumbal:~$ ssh -v prcek
OpenSSH_4.3p2 Debian-9, OpenSSL 0.9.8e 23 Feb 2007
debug1: Reading configuration data /home/ondra/.ssh/config
debug1: Applying options for prcek
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: Applying options for *
debug1: Connecting to prcek [10.28.67.33] port 22.
debug1: Connection established.
debug1: identity file /home/ondra/.ssh/id_secure_rsa type 1
debug1: Remote protocol version 2.0, remote software version OpenSSH_4.3p2 Debian-9
debug1: match: OpenSSH_4.3p2 Debian-9 pat OpenSSH*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_4.3p2 Debian-9
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: server->client aes128-cbc hmac-md5 zlib@openssh.com
debug1: kex: client->server aes128-cbc hmac-md5 zlib@openssh.com
debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(1024<1024<8192) sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_GROUP
debug1: SSH2_MSG_KEX_DH_GEX_INIT sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_REPLY
debug1: Host 'prcek' is known and matches the RSA host key.
debug1: Found key in /home/ondra/.ssh/known_hosts:32
debug1: ssh_rsa_verify: signature correct
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug1: SSH2_MSG_SERVICE_ACCEPT received

A dal uz nic. Zadna odpoved, terminal zustane viset v tomto stavu libovolne dlouho. Na prckovi se ovsem obcas objevi v /var/log/auth.log nasledujici:

Apr 19 16:59:15 prcek sshd[5774]: fatal: Timeout before authentication for 10.28.67.34

a občas i toto (nevim, jestli to s tim souvisi):

Apr 19 15:32:14 prcek sshd[5523]: Bad protocol version identification '\377\364\377\375\006\004' from UNKNOWN

pokousel jsem se
1.) menit nastaveni ssh klienta na kumbalu
2.) menit nastaveni sshd na prckovi
3.) zkusit se prihlasit obycejnym heslem
4.) vygooglovat stejny problem
5.) zkontrolovat firewally, vsechny jsou vypnute

lec bezvysledne. Z notasu se lze nadale bez problemu pripojit. Nevi nekdo, v cem tkvi problem?

Dotaz: SSH se kousne pri prihlasovani (timeout, bad protocol version)