I'm having an issue with Ubuntu Gnome 15.10 (also had the same issue with 15.04 before making a clean install of 15.10).
When closing the laptop lid, the computer shuts down instead of suspending. EDIT: It seems to suspend properly, but shuts down when trying to resume.
The tweak-tool settings are set to suspend whether power is connected or not.
I'm not sure what relevant information to provide, but I'm using a "Lenovo Flex 2" with nvidia graphics card drivers, no external monitors connected. (I've read about similar problems with external monitors)
Any help would be appreciated, thank you.