What could cause a digital circuit breaker finder to not find a breaker?
I can not help you with that particular tool.  But a word of advice.  Sometimes I have to put down my induction testor, or magnetic resonance testor and grab the radio.
plug in radio to outlet in that room and turn on high.  Turn off all breakers.
turn them back on one at a time, listen.  Do not stop if you hear the radio. Go through all the breakers.
You may have two circuits feeding that room.

Tools are nice but sometimes there is no substitute for direct observation.