Doors – How to un-stick the release button on the Yale door knob

It sounds to me like something in the knob has worn out (eg, a metal locking mechanism has broken off or been worn down). If this is the case, there's not much chance that you'll be able to [easily] fix it.

If it was me, I'd just replace the knob. You may also be able to swap it with another knob in a location where you don't need a working lock.

If I am inferring correctly what you are describing, it sounds like the "brains" of the system are installed outside with one screw access. That, of course, is an abysmal design. The only thing that should be outside accessible would be the wires to the call button and speaker - all other wiring should be inside-access only.

If you are otherwise happy with the system, you could probably move the components that should not be outside inside, leaving only the wiring needed for the outside components running to the outside box.