I have seen the sameproblem quite a few times recently and it has been the ammunition every time. Brass quality has been pretty badfrom some manufacturers. The thickness of the base or rim of the case has varied by up to .040" .The thinner cases will work fine, when one of the larger ones gets near the top it will jam between the cylinder and flash guard,(rear of frame)
Check your ammunition with a caliper, any over .045" in thickness will usually cause a jam. You can also see a case that is much thicker when you have the cylinder loaded and still out of the frame, point the muzzle down and spin the cylinder while loking at the rims. Any that look thicker should be removed.