Laptop doesn't suspend after closing lid

Basically the same question as asked in

I.e., with my recently installed Lubuntu (18.04.2), the system does not suspend after closing lid of my laptop.

sudo systemctl suspend cam make my laptop suspend, so I believe it is Lubuntu’s configuration issue.

I tried fixing the problem myself by following
i.e., uncomment the line #HandleLidSwitch=suspend from /etc/systemd/logind.conf:

$ grep HandleLidSwitch= /etc/systemd/logind.conf 

and I’ve restart the Systemd systemd-logind.service service as well.

But my laptop still doesn’t suspend after closing lid.
Please help. thx