I use command sudo pm-suspend to put my laptop to sleep and when I resume from sleep my session logs out and saved session is lost. It does not happen every time but very often.
pm-suspend-hybrid instead. It will prepare the system for hibernate by storing all memory content to disk and then goes into suspend. The suspended state gives the advantage that it can resume very quick and because it also prepared for hibernate the system is also able to start when the power is lost.