I have a 2015 Audi S3 w/ Lane Assist. With lane assist off. Sometimes while cold, sometimes after 20+ miles the steering wheel at freeway speeds will stick in the center. It's like it fights you a little bit right around center.
It seems this issue is caused by one of two things.
Problem seems to be that the sensors in the steering rack that tell the electric assist motor the position of the wheels and which way to boost the steering, left or right, are out of alignment. So there a sub-second delay in the boost, which causes the notchy feel to the steering.
Hope this is helpful.
After referencing the comments above and taking it into a different dealer, I had it confirmed that it was the rack.
It is a known issue with Audi's electric steering.
They fixed it by replacing the rack.