My HP Pavilion 15 Notebook PC (15f019dx) had the same problem after upgrading to 16.04. It would suspend from the menu with no problem, but would not suspend automatically when the lid was closed. /proc/acpi/button/lid/LID0/state was reporting the lid closed as it should. Adding HandleLidSwitchDocked=suspend to /etc/systemd/logind.conf and then rebooting fixed it.
My HP Pavilion 15 Notebook PC (15f019dx) had the same problem after upgrading to 16.04. It would suspend from the menu with no problem, but would not suspend automatically when the lid was closed. /proc/acpi/ button/ lid/LID0/ state was reporting the lid closed as it should. Adding HandleLidSwitch Docked= suspend to /etc/systemd/ logind. conf and then rebooting fixed it.