In addition, I installed new test servers Debian 9 and Debian 10

in Debian 10 everything works well, but in Debian 9 the same errors described earlier

Operating System: Debian GNU/Linux 9 (stretch)
Kernel: Linux 4.9.0-12-amd64

but if update Debian 9 OpenSSH_from version 7.4p18 to 8.1p1 then everything starts to work

x2goserver/oldstable,now amd64 [installed]
x2goserver-common/oldstable,now amd64 [installed,automatic]
x2goserver-extensions/oldstable,now all [installed,automatic]
x2goserver-fmbindings/oldstable,now all [installed,automatic]
x2goserver-printing/oldstable,now all [installed,automatic]
x2goserver-x2goagent/oldstable,now amd64 [installed,automatic]
x2goserver-xsession/oldstable,now all [installed,automatic]