I agree with Longbow. Your bow hand and arm are your problems. Try turning your bow arm elbow so that the joint is vertical rather than horizontal. If you stand with your bow extended as if you're ready to draw, then bend your bow arm elbow. If your bow comes around to your chest your elbow is correct. If the bow goes up over your head you loose stability and your bow will jump around as seen in the videos. Get your elbow in the proper position and then concentrate on holding the bow hand on target until the arrow hits.
Since we're talking form, I think you should work on getting your index finger down too. You don't need to hold the arrow on the bow if you are drawing correctly especially using 3 fingers under. But even split finger, if you need to hold the arrow on the bow you either have too much pressure on the nock or are twisting the string as you draw.
As I see it your inconsistancy is all in your bow hand and arm at this point.