Perhaps I missed it, but in this thread I haven't seen that the N-G voltage was measured on the problem branch circuit. As kwired mentioned in post #5, if the branch circuit came from a subpanel then there might be a voltage drop on its feeder neutral due to the current in other branch circuits. Although a multi-meter measures resistance by applying a DC current, measuring the resulting DC voltage, and then using R = V /I, if there was any AC voltage present that might mess up the resistance measurement. That's why the N-G voltage should be measured first to confirm that it's negligible. Since this has been a problematic case, it might be best to make a DC voltage measurement as well as an AC one on N-G.
Unless it's already been done, turning off the main breaker before making the N-G the resistance measurement should eliminate the possible neutral voltage drop issue from other circuits that's mentioned above.