Quoted from kcZ:
On occasion (more times that I'd like) the hidden hallway does not stop the ball. Lock (or extra ball) could be lit and I hit the hidden hallway but it does not lock nor register the extra ball. The ball comes around just as quick as it went in. This is a fresh restore so I assume that maybe I don't have the correct spring in that lock mech (disc coil).
any tips? I've messed around with that spring a bunch but maybe I'm missing something.
Your disc is mis-aligned, letting the ball pass through.