It's not reversed wiring. If you unplug everything on this circuit, and turn off all switches, your tester will correctly read "open neutral". Somewhere on this circuit, the white wire has become disconnected. This usually happens when a backstab of the white wire becomes loose. You may need to open up every box on the circuit (working or not) and move backstabbed connections to adjacent screws. While you're in there, tighten up any wire nuts. Start with the non-working boxes, and then move to the closest working boxes on the same circuit.