Horizontal scrolling on my touchpad was disabled upon upgrading to 17.10 and I can't find a way to re-enable it in the settings.
Two finger (horizontal and vertical) scrolling was the default behavior when I was using 16.10, even after I had switched to the GNOME desktop. However, there seems to be no settings for this both in the settings menu and dconf that I can find.
I had the same problem and couldn't find the option in
dconf-editor
(/org/gnome/desktop/peripherals/touchpad/ doesn't help). I found this command here and now horizontal scrolling seems to be working just fine. Give it a try.synclient HorizTwoFingerScroll=1
And make your fix persistent using this tip by monkbroc:
How do I make my synclient settings stick?
If you are using gnome right now,
go to settings then mouse and touchpad, in the touchpad tab set your settings like shown in the image below: