dog alert barks at apartment stairwell noises but ignores staged setups

i’m dealing with an odd training limitation with my dog and would appreciate some ideas. my dog usually barks at noises in the stairwell of my apartment building (footsteps, doors closing, people talking, keys, etc). it looks like alert barking. the catch is that he only reacts when the sounds are actually happening outside in the hallway. if i try to recreate the situation by knocking on my own door, making sounds, or playing door or hallway noise recordings, he doesn’t respond at all. same thing if someone tries to stage it without there being real hallway activity. it’s like he immediately recognizes it’s not authentic. another wrinkle is that he doesn’t always react. sometimes he’ll hear the same kind of noise and just keep resting and ignore it completely. what i’ve been trying so far: when he hears a noise and runs to the door, i start giving him treats before he starts barking and keep feeding until the noise stops. if he hears a noise but stays resting, i also give treats for that. most of the time this works fine, but occasionally he’ll get very locked in on the door and won’t take treats at all. the problem i’m running into is that the triggers are random and i can’t reliably reproduce them, which makes structured counterconditioning or desensitization hard to do. has anyone dealt with hallway or stairwell alert barking specifically? how did you approach training when the trigger only happens naturally and inconsistently?