I'm not sure what to do next, and I'm fairly inexperienced with troubleshooting home electrical issues. My investigation started with the GFCI receptacle on the kitchen counter receptacles tripping and not resetting. I replaced all the load receptacles to make sure wiring was good. I replaced and double checked the GFCI receptacle. Still tripping, even when the load was not even connected to the GFCI receptacle.
I eventually looked upstream from the GFCI and discovered that the receptacle just upstream from the GFCI was dead. I disconnected the receptacle to test the incoming voltage from the breaker. When I test the incoming line hot-to-ground I get a nice 123v, but when I test hot-to-neutral I get 109v. When I connect a receptacle to the line (not connecting the downstream load), the receptacle tester shows properly wired, but when I plug in a lamp to it, it flips to show "hot ground reversed". I've seen online that this really probably means "open neutral".
So what next? Am I on to something? Does this mean that my neutral line is compromised somewhere in the walls and losing voltage? There are several wall receptacles upstream that are all still working fine. I appreciate any thoughts.