Video was a trip - reversed. Looks like a left-side drive train. Did you shoot it sitting in front of a mirror? Looked like the teeth were not catching on the middle rear cog. Backing out the B-screw probably improved but not fully. Other other thing I might have tried would have been to slide the wheel back further in the dropouts. Hard to tell if that will help. This might give the top RD pulley more wrap on the chain and provide more lead distance to allow the chain to shift. but the other thing to check is bevel on the FW teeth. Sometimes the cog is flipped around and the bevel won't catch the chain.