In short: X2Goserver is hosted in Ubuntu 22.04 computer. It is being accessed from Ubuntu 20.04 and Windows 11. Previously, everything worked well, but today morning, I could not any more get connection to this computer, not from Ubuntu or from Windows 11.

On the Windows client error message is: "The remote proxy closed the connection while negotiating..."
On Ubuntu client, x2goclient --debug print shows:
--8<--8<--
RESUMING SESSION is KDRIVE:  false
x2go-DEBUG-../src/onmainwindow.cpp:6142> "Starting NX proxy, command: nxproxy -S nx/nx,options=/home/kalle/.x2go/S-ktuulos-50-1678441073_stDLXDE_dp24/options:50"
x2go-DEBUG-../src/sshprocess.cpp:157> Direct tunnel: waiting for connections on "localhost":34744
x2go-DEBUG-../src/onmainwindow.cpp:6618> Proxy wrote on stderr: "\nNXPROXY - Version 3.5.99.23\n\nCopyright (c) 2001, 2011 NoMachine (http://www.nomachine.com)\nCopyright (c) 2008-2014 Oleksandr Shneyder <o.shneyder@phoca-gmbh.de>\nCopyright (c) 2014-2016 Ulrich Sibiller <uli42@gmx.de>\nCopyright (c) 2014-2016 Mihai Moldovan <ionic@ionic.de>\nCopyright (c) 2011-2016 Mike Gabriel <mike.gabriel@das-netzwerkteam.de>\nCopyright (c) 2015-2016 Qindel Group (http://www.qindel.com)\n\nNXCOMP, NX protocol compression and NX extensions to this software\nare copyright of the aforementioned persons and companies.\n\nRedistribution and use of the present software is allowed according\nto terms specified in the file LICENSE.nxcomp which comes in the\nsource distribution.\n\nAll rights reserved.\n\nNOTE: This software has received contributions from various other\ncontributors, only the core maintainers and supporters are listed as\ncopyright holders. Please contact us, if you feel you should be listed\nas copyright holder, as well.\n\nNX protocol compression is derived from DXPC project.\n\nCopyright (c) 1995,1996 Brian Pane\nCopyright (c) 1996,1997 Zachary Vonler and Brian Pane\nCopyright (c) 1999 Kevin Vigor and Brian Pane\nCopyright (c) 2000,2003 Gian Filippo Pinzari and Brian Pane\n\nAll rights reserved.\n\nSee https://github.com/ArcticaProject/nx-libs for more information.\n\nInfo: Proxy running in server mode with pid '2505200'.\nSession: Starting session at 'Fri Mar 10 11:37:54 2023'.\nInfo: Using errors file '/home/kalle/.x2go/S-ktuulos-50-1678441073_stDLXDE_dp24/sessions'.\nInfo: Using stats file '/home/kalle/.x2go/S-50/stats'.\nLoop: WARNING! Overriding auxiliary X11 port with new value '1'.\nWarning: Overriding auxiliary X11 port with new value '1'.\nInfo: Using abstract X11 socket in kernel namespace for accessing DISPLAY=:50.\nInfo: Connecting to remote host 'localhost:34744'.\nInfo: Connected to remote proxy on FD#5.\n"
x2go-DEBUG-../src/sshprocess.cpp:109> New TCP connection.
x2go-DEBUG-../src/sshprocess.cpp:114> New socket: 14
x2go-DEBUG-../src/sshmasterconnection.cpp:1977> Creating new channel.
x2go-DEBUG-../src/sshmasterconnection.cpp:1990> New channel:0x7f41a4012000
x2go-DEBUG-../src/sshmasterconnection.cpp:1994> Forwarding parameters: from remote ("localhost":33744) to local ("localhost":33758)
x2go-DEBUG-../src/sshmasterconnection.cpp:2028> Temporary session port after config file parse: 33744
x2go-DEBUG-../src/sshmasterconnection.cpp:2032> Temporary session host after config file parse: localhost
x2go-DEBUG-../src/sshmasterconnection.cpp:2059> New channel forwarded.
....
x2go-DEBUG-../src/sshmasterconnection.cpp:2121> EOF on channel 0x7f41a4012000; SshProcess object: 2
x2go-DEBUG-../src/sshmasterconnection.cpp:2222> EOF sent.
x2go-DEBUG-../src/sshmasterconnection.cpp:2224> Channel closed.
x2go-DEBUG-../src/onmainwindow.cpp:6618> Proxy wrote on stderr: "Loop: PANIC! The remote NX proxy closed the connection.\nError: The remote NX proxy closed the connection.\nLoop: PANIC! Failure negotiating the session in stage '7'.\nError: Failure negotiating the session in stage '7'.\nLoop: PANIC! Wrong version or invalid session authentication cookie.\nError: Wrong version or invalid session authentication cookie.\nSession: Terminating session at 'Fri Mar 10 11:37:59 2023'.\nSession: Session terminated at 'Fri Mar 10 11:37:59 2023'.\nqt.qpa.xcb: X server does not support XInput 2\n"
x2go-DEBUG-../src/onmainwindow.cpp:6475> Deleting Proxy.
x2go-DEBUG-../src/onmainwindow.cpp:6520> Waiting for proxy to exit.
x2go-DEBUG-../src/onmainwindow.cpp:6544> Checking exit status.
x2go-DEBUG-../src/sshprocess.cpp:199> Executing remote command via SshProcess object 3: "x2gocmdexitmessage ktuulos-50-1678441073_stDLXDE_dp24"
--8<--8<--

Printing, audio and shared folder have previously been activated and they have worked. Now I have disabled them and it does not make any difference.

I have tried to re-install x2go server by command:
sudo apt-get install --reinstall x2goserver x2goserver-common x2goserver-xsession

On the server computer, .xsession-x2go-<client>-errors file has following:
--8<--8<--
XSession-x2go: X session started for ktuulos at pe 10.3.2023 11.30.25 +0200
dbus-update-activation-environment: setting DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/1000/bus
dbus-update-activation-environment: setting DISPLAY=:50
dbus-update-activation-environment: setting XAUTHORITY=/home/ktuulos/.Xauthority
xrdb: Connection reset by peer
xrdb: Can't open display ':50'
/etc/x2go/Xsession.d/30x11-common_xresources: line 16: has_option: command not found
xhost:  unable to open display ":50"
/etc/x2go/Xsession.d/75dbus_dbus-launch: line 9: has_option: command not found
dbus-update-activation-environment: setting QT_ACCESSIBILITY=1
/etc/x2go/Xsession.d/90x11-common_ssh-agent: line 9: has_option: command not found
dbus-update-activation-environment: setting SHELL=/bin/bash
--8<--8<--

X2goserver host information:
ktuulos@kallep50:~$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 22.04.2 LTS
Release: 22.04
Codename: jammy
ktuulos@kallep50:~$ dpkg -l x2go* openssh-server
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name                  Version         Architecture Description
+++-=====================-===============-============-===================================
ii  openssh-server        1:8.9p1-3ubuntu0.1 amd64        secure shell (SSH) server, for secure access from remote machines
un  x2goagent             <none>             <none>       (no description available)
ii  x2goclient            4.1.2.2-2build1    amd64        X2Go Client application (Qt5)
un  x2goclient-gtk        <none>             <none>       (no description available)
un  x2godesktopsharing    <none>             <none>       (no description available)
un  x2goprint             <none>             <none>       (no description available)
ii  x2goserver            4.1.0.3-5          amd64        X2Go Server
ii  x2goserver-common     4.1.0.3-5          all          X2Go Server (common files)
un  x2goserver-compat     <none>             <none>       (no description available)
ii  x2goserver-extensions 4.1.0.3-5          all          X2Go Server (extension support)
ii  x2goserver-fmbindings 4.1.0.3-5          all          X2Go Server (file manager bindings)
un  x2goserver-home       <none>             <none>       (no description available)
un  x2goserver-one        <none>             <none>       (no description available)
ii  x2goserver-printing   4.1.0.3-5          all          X2Go Server (printing support)
un  x2goserver-pyhoca     <none>             <none>       (no description available)
ii  x2goserver-x2goagent  4.1.0.3-5          amd64        X2Go Server's X2Go Agent
ii  x2goserver-xsession   4.1.0.3-5          all          X2Go Server (Xsession runner)

On the Ubuntu 20.04 version, x2go package versions are the same, but openssh-server is version 1:8.2.

Could someone please instruct how to get this working? This Ubuntu 22.04 is my R&D work computer and I don't have a keyboard or monitor attached to it at all, so now I can only use it through the SSH terminal, which makes desktop operations pretty difficult. :(

BR
  Kalle