I once had this issue - I believe it was last May - as I was flying DEL-YYZ. The SD had no clue what to do so he went to the cockpit and the FO came in, sat in my seat and did the reset procedure. I offered to sit in the jumpseat if the procedure didn't work. The seat reinflated and was initially fine but I had to reset it at least three times over this 14-hour flight. I have also had this happen on at least another flight in the last year but never bothered to write to CS for any of these two cases.