Hibernation and Sleep mode not working as expected

Every time I try sleep mode computer won't partially shut down as expected, it just log out. Similar strange behaviour apply to hibernation mode when computer restarts instead of shutting down (yes, my computer is capable of hibernation). However, shutting down or logging out works fine. I'm using Ubuntu 18.04 with Xfce for several months already and I'm happy with it but this thing driving me crazy because back in windows I was using hibernation mode a lot and I'd like to keep this style of workflow.I wish to tell you more but I really don't know what is happening on background or what causing it. Although I didn't told you much, I told you everything I know about this problem.