sleep-monitor system is about to suspend

On a remote Linux server running XFCE desktop, the server goes down randomly, on monitoring /var/log/syslog, i found the following message

Jan 18 05:43:24 sokdesk ModemManager[1300]:   [sleep-monitor] system is about to suspend
Jan 18 05:43:24 sokdesk systemd[1]: Reached target Sleep.
Jan 18 05:43:24 sokdesk systemd[1]: Starting Record successful boot for GRUB...
Jan 18 05:43:24 sokdesk systemd[1]: Starting Suspend...
Jan 18 05:43:24 sokdesk systemd-sleep[2574]: Suspending system...
Jan 18 05:43:24 sokdesk kernel: [ 1217.283955] PM: suspend entry (s2idle)

When this happens, the remote desktop and SSH connections to the server get disconnected. To get back to the server, I had to restart the server.

The error is fixed by running the command

systemctl mask sleep.target suspend.target hibernate.target hybrid-sleep.target