Why can I no longer turn the knob of my self-locking door from the inside?
There's a pivot joint in the middle of the knob shaft which lets the two ends rotate relative to each other. You need to get things lined up so each end of the shaft engages just its side of the lockset. That may take some experimentation to get the amount screwed into each of the knobs just right to balance this out, though the cross-pin should help you find the right position.