Pair of 12/3 wires in outlet box showing neutral-ground voltage
Harper is right about trace voltages on disconnected wires it could be anything causing inductance in the wires, but there are few things that concern me.

Aluminum wiring: One of the big problems with aluminum branch wiring is that is has a tendency to loosen up on connections and burn back from the connection point. Then you will be getting weird voltage readings like 57.7 volts. But I don't think this is the case where you have a red and a black reading the same voltage more than likely they have no power connected to them and should be reconnected to the other red and black with 128.4 volts. 

You didn't mention if everything was working before you started your pigtail. When you start taking things apart you can start finding things like you have mentioned and we get caught up in chasing ghosts. 

Instead of trying to determine each problem as you go along, I would complete the pigtailing first. Then go through and turn everything on and check to see if there are any problems. Look for strange things like a 1 or 2 volt drop between two receptacles that are only say 12' apart. That would indicate a loose connection somewhere. Lights dimming when you turn something on and the circuits are not related. That would indicate a loose or broken neutral. You television only comes on when the dryer is running (true story). Also broken neutral.

Then if you find something acting up you can identify the physical problem and location. Then if you post that problem we can be proactive and not so speculative.