Recently I upgraded to 18.04 LTS and found that the secondary key (right click key) of the touchpad isn't responding, but while using external mouse all things seems fine.
I tried disabling two finger from Gnome tweak tool even tried adding
Option "ClickPad" "true" Option "EmulateMidButtonTime" "0"
70-synaptics.conf, but it still did not work. I also tried setting mouse emulator to area through tweak tool.