FWIW I have the problem on my 2018 SS w/ A8. Build date is 08/17. Happened within the first 1,000 miles. Dealership did the flush and threw in a couple extras like crushing those areas behind the front wheels where you are NOT supposed to lift the car from. As those areas collapsed, it let the rockers hit the lift arms and luckily it only messed up the bottom of the rockers that can't be seen unless you’re under the car. I have 1,500ish miles and the shudder is still there. The flush never completely fixed it, I'd say 90% improvement at first. The problem is always there but, is worse when the trans fluid is up to temp. Another thing that will get it going easily is when I'm at 25~50mph and it upshifts sort of at the same time I press the accelerator pedal a little to increase my speed.... kind of like it's shifting right into the shudder.
I'm probably going to get a CircleD or Yank converter and have a well-known local shop install it. The way I look at it is what good is a warranty if your car comes back in worse shape than before it went in for service. I love the car but, the shudder is driving me
