One thing that can cause the type of problems you are describing is the adjustment of the twine fingers. they need to be set so the point is part way over the slot in the top of the bale chamber, but not so far that they interfere with the twine on the underside of the needle, and also set so that there is minimal clearance betweenthe underside of the needle and the twine finger as the needle comes into the knotter assy. and the twine finger moves through it's arc. One other cause can be worn slides on the plunger or the chamber, i.e. too much clearance between the top of the plunger and the bale chamber. One more, if possible compare the twine finger cam length to an unworn one, a worn one will not move the twine finger cams far enough and cause the knots to hang on the bill hook.
Thats my epistle for the night, good luck. Harry