Linux – Arch sometimes won’t suspend

Sometimes the computer won't auto-suspend when the lid has been closed. When this happens re-closing the lid won't make it suspend until next reboot. After the reboot the auto-suspend works again. After a while it stops working again, I haven't been able to determine what changes the state from suspendable to unsuspendable.

In the unsuspendable state "sudo pm-suspend" and "sudo systemctl suspend" don't make it stay suspended.

I'm running a Lenovo X220 with Arch 64 bit.

What should I do/try to make it work as it is supposed to?

EDIT:added journalctl output:

journalctl -xn

-- Logs begin at Sun 2013-08-25 11:05:23 CEST, end at Tue 2014-03-04 20:32:31 CET. --
Mar 04 20:32:06 x220 systemd[1]: systemd-suspend.service: main process exited, code=exited, status=1/FAILURE
Mar 04 20:32:06 x220 systemd[1]: Failed to start Suspend.
-- Subject: Unit systemd-suspend.service has failed
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- Documentation: http://www.freedesktop.org/wiki/Software/systemd/catalog/be02cf6855d2428ba40df7e9d022f03d
-- 
-- Unit systemd-suspend.service has failed.
-- 
-- The result is failed.
Mar 04 20:32:06 x220 systemd[1]: Dependency failed for Suspend.
-- Subject: Unit suspend.target has failed
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- Documentation: http://www.freedesktop.org/wiki/Software/systemd/catalog/be02cf6855d2428ba40df7e9d022f03d
-- 
-- Unit suspend.target has failed.
-- 
-- The result is dependency.
Mar 04 20:32:06 x220 systemd[1]: Service sleep.target is not needed anymore. Stopping.
Mar 04 20:32:06 x220 systemd[1]: Unit systemd-suspend.service entered failed state.
Mar 04 20:32:06 x220 systemd[1]: Stopping Sleep.
-- Subject: Unit sleep.target has begun shutting down
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit sleep.target has begun shutting down.
Mar 04 20:32:06 x220 systemd[1]: Stopped target Sleep.
-- Subject: Unit sleep.target has finished shutting down
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- Documentation: http://www.freedesktop.org/wiki/Software/systemd/catalog/9d1aaa27d60140bd96365438aad20286
-- 
-- Unit sleep.target has finished shutting down.
Mar 04 20:32:06 x220 sudo[21989]: pam_unix(sudo:session): session closed for user root
Mar 04 20:32:06 x220 kernel: video LNXVIDEO:00: Restoring backlight state