pm-suspend gives the appearance of putting the machine to sleep.  However, when the wake button is pressed, the machine goes through the following actions: it powers down (cutting power to peripherals), it powers on but doesn't get to POST, it powers down again, then it goes through a normal power on and cold boot sequence.  No session states appear to be saved.  What should happen is that the machine wakes up on the first try and that all states are restored without rebooting.  

This is on a System76 GazellePro 9 with and 8-core Intel(R) Core(TM) i7-4810MQ CPU @ 2.80GHz

dmesg includes this :

 [    2.382494] PM: Starting manual resume from disk
 [    2.382497] PM: Hibernation image partition 259:0 present
 [    2.382498] PM: Looking for hibernation image.
 [    2.382655] PM: Image not found (code -22)
 [    2.382657] PM: Hibernation image not present or could not be loaded.

pm-suspend-hyrbid and pm-hibernate usually restore the machine's states.  When saving, the machine appears to power down, turns on again with the states intact, then finally powers down for good.  When resuming, pm-suspend-hyrbid and pm-hibernate go through the same conniptions described above when trying to wake up from pm-suspend, however with the one difference that the states finally are restored.  Lastly, though the session is available the screen lock kicks in after some seconds and that must be unlocked to continue.  That should have been locked from the start of the resume.  

$ apt-cache policy xfce4-power-manager
xfce4-power-manager:
  Installed: 1.4.1-1
  Candidate: 1.4.1-1
  Version table:
 *** 1.4.1-1 0
        500 http://fi.mirror.devuan.org/merged/ jessie/main amd64 Packages
        100 /var/lib/dpkg/status

$ uname -s -r -v -p -o
Linux 3.16.0-4-amd64 #1 SMP Debian 3.16.39-1 (2016-12-30) unknown GNU/Linux

$ lsb_release -rd
Description:	Devuan GNU/Linux 1.0 (jessie)
Release:	1.0