After upgrading to Ubuntu 16.04 LTS, my laptop stopped moving to standby mode. The screen just goes blank, but the laptop continues to work, it stops responding to any actions by the user. From this state it can not be withdrawn, only by restarting through the power button.
Hp pavilion dv6 6169er laptop. In Ubuntu 15.10, everything worked fine.
After installation, I cleaned the system of unused packages and deleted the old kernels. Perhaps after these actions, I accidentally deleted the library responsible for the correct transition to the "standby mode", but this is only an assumption, everything was done through the standard package manager.