S&W might or might not indicate what the problem was after they fix it.
Well, my thinking was that if the cylinder did hang up due to heat expansion of the cylinder, the hand might be hanging on the ratchet for the same reason. If the ratchet tooth expands, a tightly fitted hand might not have enough room to drop down so the trigger would not return.
Of course, I could be all wet, but I have seen several cases of revolvers that hung up after firing 10-20 rounds, then were fine when they cooled down; the problem was always the b/c gap. (Most folks get up tight about too great a gap; few consider that too little a gap might be bad also. FWIW, I consider .007-.008" just about right.)