Sounds like the nub and the arm are applying too much pressure when they are installed. Not trying to insult your intelligence, but make sure there is not too much hop up pressure on the bucking, which in turn puts too much pressure on the bb. So make sure that the nub is not too big for your particular chamber. Even if it is a clone, the nub might be too big and causes too much pressure. On mine, I used a nub that was wayyy too big and caused jams exactly like you described.
Have you tried it with the hop up on the lowest setting possible?
Also, be sure that the bucking is centered correctly. Had this issue when I first started with bolt action rifles. Bucking would not be aligned properly and even the slightest misalignment could cause the same exact issues as you.
Hope this helps somewhat. I realize this is a pain in the ass, and will try and help you come up with a solution.
Have you tried it with the hop up on the lowest setting possible?
Also, be sure that the bucking is centered correctly. Had this issue when I first started with bolt action rifles. Bucking would not be aligned properly and even the slightest misalignment could cause the same exact issues as you.
Hope this helps somewhat. I realize this is a pain in the ass, and will try and help you come up with a solution.