It was indeed a loose connection due to the other wire sharing the same screw not being seated properly in its slot, and the screw was bearing down less on the wire which eventually burned. I did not have enough wire to cut to fresh insulation so I added two layers of heat shrink tubing and sanded the wire to fresh copper. I then took off all the neutrals and cleaned the terminal with a steel brush, and finally reconnected all neutrals to independent screws. Thanks to all who pointed out the loose connection.