Formkey validation is not enabled. I was on 220.127.116.11 and everything was running perfectly. Now, after the upgrade, checkout just won't move to Step 3. I hit continue, it says loading next step and doesn't go to the next step no matter how many times you hit continue.
There were several reports of that kind. I'm not sure about one final soolution becuase I've saw different problems/solutions several times.
Maybe this links can help you to start: