to narrow down this issue, please try these steps:

1 o enable loglevel=debug in /etc/x2go/x2goserver.conf, what do you see in
/var/log/messages?
2 o use a Linux X2Go Client
3 o use PyHoca-GUI or PyHoca-CLI as client application for X2Go on a Linux
machine (with --libdebug option on the cmdline)
4 o btw. do you actually see the session window (for desktop sessions)
appear? (and then disappear?)
5 o try ssh user@server -X nxagent :20 (does nxagent come up?)

We have to find out, if your crash is an X2Go Server bug or an NX bug on EPEL-7.

Thanks+Greets,
Mike

1- /var/log/message with debug loglevel on server after a try with a Windows client:
Dec 11 21:24:42 centos7nightly systemd: Created slice user-1000.slice.
Dec 11 21:24:42 centos7nightly systemd: Starting Session 3 of user jasminl.
Dec 11 21:24:42 centos7nightly systemd: Started Session 3 of user jasminl.
Dec 11 21:24:42 centos7nightly systemd-logind: New session 3 of user jasminl.
Dec 11 21:24:45 centos7nightly systemd-logind: Removed session 3.

2- On a CentOS 7 machine, with x2goclient:

x2go-INFO-1> "Starting x2goclient..."
x2go-WARNING-1> "Can't load translator: :/x2goclient_en_us"
x2go-WARNING-2> "Can't load translator: :/qt_en_US"
x2go-INFO-3> "Started x2goclient."
x2go-INFO-8> "Starting connection to server: 10.10.1.147:22"
Segmentation fault (core dumped)

3-On a CentOs 7 machine, PyHoca-GUI rpm dependency boken with epel... requires notify-python, PyHoca-CLI installs successfully (will created another bug for that one..) so...
Calling "pyhoca-cli --server 10.10.1.147 --libdebug -q lan --password mypass":
Traceback (most recent call last):
File "/usr/bin/pyhoca-cli", line 422, in <module>
    thisPyHocaCLI.authenticate()
File "/usr/lib/python2.7/site-packages/pyhoca/cli/frontend.py", line 455, in authenticate
    self._X2GoClient__connect_session(self.x2go_session_hash, username=_username, password=self.args.password, force_password_auth=force_password_auth)
File "/usr/lib/python2.7/site-packages/x2go/client.py", line 1367, in connect_session
    sshproxy_force_password_auth=sshproxy_force_password_auth,
File "/usr/lib/python2.7/site-packages/x2go/session.py", line 1355, in connect
    self.update_status()
File "/usr/lib/python2.7/site-packages/x2go/session.py", line 1641, in update_status
    raise e
x2go.x2go_exceptions.X2GoControlSessionException: x2golistsessions command failed after we have tried 20 times

In the server's /var/log/message:
Dec 11 22:05:33 centos7nightly systemd: Starting Session 14 of user jasminl.
Dec 11 22:05:33 centos7nightly systemd-logind: New session 14 of user jasminl.
Dec 11 22:05:33 centos7nightly systemd: Started Session 14 of user jasminl.
Dec 11 22:05:33 centos7nightly /usr/bin/x2gofeaturelist: x2gofeaturelist called with options:
Dec 11 22:06:00 centos7nightly systemd: Failed to mark scope session-14.scope as abandoned : Stale file handle
Dec 11 22:06:00 centos7nightly systemd-logind: Removed session 14.

While trying to run x2golistsessions on the server:
DBIconnect('dbname=/var/x2go/x2go_sessions','',...)failed:unabletoopendatabasefileat/usr/share/perl5/vendor_perl/X2Go/Server/DB/SQLite3.pmline67.

Could it be possible that the DB was never created / initialized during x2goserver's install process? or is it something else entirely? Am I using pyhoca-cli correctly?

4- No, I don't see the same behavior as with bug #675

5- Yes, if by nxagent you mean a black empty window with NX as the title.

Thanks for the followups

Jasmin