System Preferences > Trackpad > Point & Click > "Tap to Click" is disabled even if the checkbox corresponding to it is checked, to fix it i created an apple script that enable it and if it's already enabled it than it unchecked and checked it again

applescript: fix tap to click on osx sierra

tell application "System Preferences"
	activate
	set current pane to pane "com.apple.preference.trackpad"
end tell

tell application "System Events"
	tell process "System Preferences"
		repeat until exists tab group 1 of window "Trackpad"
		end repeat
		
		tell tab group 1 of window "Trackpad"
			click radio button "Point & Click"
		end tell
		
		set theCheckbox to checkbox 2 of tab group 1 of window "Trackpad"
		
		tell theCheckbox
			set checkBoxStatus to value of theCheckbox as boolean
			if checkBoxStatus is false then
				click theCheckbox
			else
				click theCheckbox
				click theCheckbox
			end if
			# Set to "if checkBoxStatus is true" to disable
		end tell
		
	end tell
end tell

tell application "System Preferences"
	quit
end tell