EDIT: I previously thought this was related to mouse, but I have been experiencing these issues without a mouse plugged-in during the past weeks. I therefore rewrote the description.
The two-finger scrolling on my UX31 works just fine, but sometimes it stops working, the cause is unknown. Multitouch also breaks whenever I go in sleep mode.
Logging out and back in fixes the issue, till it happens again (sleep, or the unknown source)
Does this sound familiar to anyone here?