Same experience with my 2012 SR. Occurs from time to time and then goes away. I tried to lub the mech under the hood with some kind of WD40.
never use WD40 lube for the shifting mechanism. Only white grease or some sort of waterproof grease. If you have experience in rebuilding shifter , you can take it apart , clean , regrease. that's it. Most of the time its easier to just replace the whole body if its still under warranty.
I had the same problem when my 2011 SR was newer, but now it's quite rare. I called Campy N.A. and explained the issue. I was told 2 things: Check the hood alignment in relation to the thumb lever, and that while riding my hands put pressure on the shifters (thumb and finger levers) which causes the jamming. Campy told me to try shifting the opposite lever to free to jam.
I know the hoods are not a problem and my hand pressure is negligible. Honestly, if this many people are having the same issue there's a bigger problem going on. (Funny, I started a thread a couple years ago on this issue and no one had any experience with it?..)
I've seen the same thing as what Campy NA told you. Sometimes the hood will block the travel of the thumb lever. It doesn't retract fully and can cause the locking. You can fix the problem by cutting the excess rubber of the hood with an x acto blade till there is no interference.
Second thing is user error. people that ride with their thumb on the shifter paddle. That's a bad habit.
Third, the shifter is defective and is replaced under warranty. With the new ultra shift , Campy no longer has the parts available separately , so campy now sells the body with mechanism. Its a 5 minute job. Swap the brake lever and hood and your good to go. I see more defective shifters with SR than record or chorus.