I would be curious as to whether the notch in the ejector shank is deep enough for the ejector stop pin/lever pin to retain the ejector. I would assemble all the parts including the stop pin into the breechblock with the breechblock out of the rifle. Note the position of the parts and try to determine if the ejector shank can jump the stop pin. Might use an empty cartridge case or wood dowel to manipulate the ejector a dozen times or more to see if the ejector malfunctions. If you have all the parts and have them assembled correctly, that's the approach I would take to diagnose the problem. Hope this cures your problem.