"System program problem detected" error

Another lightdm error here:

ERROR: apport (pid 5527) Thu Feb 28 13:14:52 2019: executable: /usr/sbin/lightdm (command line "lightdm --session-child 13 20")

ERROR: apport (pid 5527) Thu Feb 28 13:14:52 2019: is_closing_session(): no DBUS_SESSION_BUS_ADDRESS in environment

ERROR: apport (pid 5527) Thu Feb 28 13:14:53 2019: wrote report /var/crash/_usr_sbin_lightdm.0.crash,