Trackpad two finger scrolling and right-click issue with Ubuntu 17.10 (i386, 64bit, GNOME 3.26.1) on a Lenovo T540p (the model with a Intel Core i5-4210M Haswell CPU etc)
I have the same issue on my Thinkpad T450s. This issue is referenced on launchpad here: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1722478
It seems to happen after a resume. The workaround described on LP1722478 works for me:
sudo modprobe -r psmouse sudo modprobe psmouse
Update for other ThinkPad users, as per the hard work done here, the workaround is as follows...
Edit the file
/etc/default/grub and change the line:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash psmouse.synaptics_intertouch=0"
You probably were using Unity as your desktop environment before and are using Gnome Shell now. (Whether you wanted it or not, the upgrade decided for you.)
If you want to use Unity even now, that is an option, and it will resolve your problem. You may already have Unity installed, whether you know it or not, but in case you don't:
sudo apt install unity
Then when you restart and select your user on the login screen, don't enter your password right away. Instead, notice the little gear icon by your 'Sign in' button. Click it, and you should see that you have a choice between 'Ubuntu', 'Ubuntu on Xorg', and 'Unity'. Click 'Unity', then sign in with your password as usual.
I recommend this for users who want to go back to the environment they had before.