My receptacle tester is giving confusing results, what should I do?
That would seem to indicate a failing neutral connection, if you get a voltage tester it will likely report something well below 120v. You'll need to trace the circuit back to find the point where the neutral first fails and then check the connections for anything loose or arcing. If you can't find any bad connections on either end, then it could be a nail or faulty wiring and you'll need to replace that section of the circuit.