@Emma1989: See my answer to @JohnWis above:

I have sent you the modified version only for your "analysis", if you indeed suffer from the referenced problem. It was not meant to be a solution. The solution is to upgrade your OpenSSH installation.

martin wrote:

Upgrade your OpenSSH installation.
Or, if you register, I can send you a copy of WinSCP that does not trigger the wrong rule.

Can you please send this to me also I cannot get it to work for me at all- emma181111@hotmail.com

I have sent you the modified version only for your "analysis", if you indeed suffer from the referenced problem. It was not meant to be a solution. The solution is to upgrade your OpenSSH installation.

Hello, in the past I get from you a changed version of WinSCP without the issue, can you give us a new updated mobile version without the issue?

Sent.

I just registered, can you send me a copy of WinSCP that does not trigger the wrong rule.

Upgrade your OpenSSH installation.
Or, if you register, I can send you a copy of WinSCP that does not trigger the wrong rule.

What should we do to analyse or solve if this is the problem we have.

I believe there was no change in those versions that might have caused this.
But you might be suffering from this glitch in OpenSSH:
https://bugzilla.mindrot.org/show_bug.cgi?id=2748
I have added this issue to the documentation:
https://winscp.net/eng/docs/incompatible_changes#older_general

Tested again
Version 5.9.6 is OK
Version 5.10.4.RC NOK
Version 5.11 is NOK

So there is a difference after version 5.9.6

JohnWis wrote:

Do you want us to try the versions between 5.9.3 and 5.10?

Yes please.

We already did

Version 5.9.3 ok
Version 5.10 Nok
Version 5.17.6 Nok

Do you want us to try the versions between 5.9.3 and 5.10?

Can you try to find out, what version did introduce the problem?
https://sourceforge.net/projects/winscp/files/WinSCP/

The log file from the linux server gives this message:

Sshd_config server

And WinSCP should support this, but is this still in the current release
https://winscp.net/eng/docs/tls_ciphersuites

Thanks for the log. It didn't reveal anything useful though. Did you have an access to server-side logs? Don't you need to whitelist the new version somehow in your "XenApp environment"?

Old log file added

Can you post a log file of a successful session from the old version of WinSCP?

WinSCP version 5.17.6
Worked with version 5.9.3
Windows server 2016 (in Citrix)
SFTP
Using the GUI
Error:

Remote side unexpectedly closed network connection

or:

Network error: Software caused connection abort

When setting up a connection to a Linux server, an error occur, connection can't be establised.
With the old version of WinSCP there is no issue to connect to these Linux servers, It is not 1 server but a pool of servers not working.
The WinSCP client (old en new) are running on a XenApp environment.