Comment 2 for bug 1699637

I'm having the exact and/or similar problem, but I'm running on an Arch based distro. My Log is as follows:

[+0.09s] DEBUG: Logging to /var/log/lightdm/lightdm.log
[+0.09s] DEBUG: Starting Light Display Manager 1.24.0, UID=0 PID=488
[+0.09s] DEBUG: Loading configuration dirs from /usr/share/lightdm/lightdm.conf.d
[+0.09s] DEBUG: Loading configuration dirs from /usr/local/share/lightdm/lightdm.conf.d
[+0.09s] DEBUG: Loading configuration dirs from /etc/xdg/lightdm/lightdm.conf.d
[+0.09s] DEBUG: Loading configuration from /etc/lightdm/lightdm.conf
[+0.09s] DEBUG: Registered seat module local
[+0.09s] DEBUG: Registered seat module xremote
[+0.09s] DEBUG: Registered seat module unity
[+0.09s] DEBUG: Using D-Bus name org.freedesktop.DisplayManager
[+0.09s] DEBUG: Monitoring logind for seats
[+0.09s] DEBUG: New seat added from logind: seat0
[+0.09s] DEBUG: Seat seat0: Loading properties from config section Seat:*
[+0.09s] DEBUG: Seat seat0: Starting
[+0.09s] DEBUG: Seat seat0: Creating greeter session
[+0.15s] DEBUG: Seat seat0: Creating display server of type x
[+0.15s] DEBUG: Could not run plymouth --ping: Failed to execute child process “plymouth” (No such file or directory)
[+0.15s] DEBUG: Using VT 7
[+0.15s] DEBUG: Seat seat0: Starting local X display on VT 7
[+0.15s] DEBUG: XServer 0: Logging to /var/log/lightdm/x-0.log
[+0.19s] DEBUG: XServer 0: Writing X server authority to /run/lightdm/root/:0
[+0.19s] DEBUG: XServer 0: Launching X Server
[+0.19s] DEBUG: Launching process 497: /usr/bin/X :0 -seat seat0 -auth /run/lightdm/root/:0 -nolisten tcp vt7 -novtswitch
[+0.19s] DEBUG: XServer 0: Waiting for ready signal from X server :0
[+0.19s] DEBUG: Acquired bus name org.freedesktop.DisplayManager
[+0.19s] DEBUG: Registering seat with bus path /org/freedesktop/DisplayManager/Seat0
[+3.10s] DEBUG: Loading users from org.freedesktop.Accounts
[+3.10s] DEBUG: User /org/freedesktop/Accounts/User1000 added
[+7.73s] DEBUG: Got signal 10 from process 497
[+7.73s] DEBUG: XServer 0: Got signal from X server :0
[+7.73s] DEBUG: XServer 0: Connecting to XServer :0
[+7.73s] CRITICAL: g_object_unref: assertion 'G_IS_OBJECT (object)' failed
[+7.73s] DEBUG: Seat seat0: Display server ready, starting session authentication
[+7.73s] DEBUG: Session pid=524: Started with service 'lightdm-greeter', username 'lightdm'
[+7.94s] DEBUG: Session pid=524: Authentication complete with return value 0: Success
[+7.94s] DEBUG: Seat seat0: Session authenticated, running command
[+7.95s] DEBUG: Launching process 527: /usr/bin/numlockx on
[+8.03s] DEBUG: Process 527 exited with return value 0
[+8.03s] DEBUG: Seat seat0: Exit status of /usr/bin/numlockx on: 0
[+8.03s] DEBUG: Session pid=524: Running command /usr/bin/lightdm-gtk-greeter
[+8.03s] DEBUG: Creating shared data directory /var/lib/lightdm-data/lightdm
[+8.03s] DEBUG: Session pid=524: Logging to /var/log/lightdm/seat0-greeter.log
[+8.47s] DEBUG: Activating VT 7
[+8.47s] DEBUG: Activating login1 session c1
[+8.47s] DEBUG: Seat seat0 changes active session to c1
[+8.47s] DEBUG: Session c1 is already active
[+10.95s] DEBUG: Greeter connected version=1.24.0 api=1 resettable=false
[+12.80s] DEBUG: Greeter start authentication for kool
[+12.80s] DEBUG: Session pid=598: Started with service 'lightdm', username 'kool'
[+13.03s] DEBUG: Session pid=598: Got 1 message(s) from PAM
[+13.03s] DEBUG: Prompt greeter with 1 message(s)
[+22.27s] DEBUG: Continue authentication
[+22.30s] DEBUG: Session pid=598: Authentication complete with return value 0: Success
[+22.30s] DEBUG: Authenticate result for user kool: Success
[+22.30s] DEBUG: User kool authorized
[+22.36s] DEBUG: Greeter requests session xfce
[+22.37s] DEBUG: Seat seat0: Stopping greeter; display server will be re-used for user session
[+22.37s] DEBUG: Terminating login1 session c1
[+22.37s] DEBUG: Session pid=524: Sending SIGTERM
[+22.66s] DEBUG: Greeter closed communication channel
[+22.66s] DEBUG: Session pid=524: Exited with return value 0
[+22.66s] DEBUG: Seat seat0: Session stopped
[+22.66s] DEBUG: Seat seat0: Greeter stopped, running session
[+22.66s] DEBUG: Registering session with bus path /org/freedesktop/DisplayManager/Session0
[+22.66s] CRITICAL: g_object_unref: assertion 'G_IS_OBJECT (object)' failed
[+22.66s] DEBUG: Session pid=598: Running command /etc/lightdm/Xsession startxfce4
[+22.67s] DEBUG: Creating shared data directory /var/lib/lightdm-data/kool
[+22.67s] DEBUG: Session pid=598: Logging to .xsession-errors
[+23.26s] DEBUG: Activating VT 7
[+23.26s] DEBUG: Activating login1 session c2
[+23.26s] DEBUG: Seat seat0 changes active session to
[+23.26s] DEBUG: Seat seat0 changes active session to c2
[+23.26s] DEBUG: Session c2 is already active