We recently bought a house and then we found one of the outlet in master bedroom doesn't work. The lower outlet has power but the upper outlet doesn't.
After open the cover plate, I found the copper bridge on the hot wire side is broken. There is a red wire connecting the upper hot side, a white wire connecting upper neutral side, another white connecting bottom neutral side, a black wire connecting bottom hot side. The other side of black wire is connecting with another black wire using a wiring nut.
There are two wall switches, one is for the ceiling fan and the other one is for recess light. I guess the red one was from the switch and later when the previous owner change the switch to control the ceiling fan or recess light, the red wire is abandoned. My fix is replace the outlet with a new one, connect black wire to bottom hot side, white to bottom neutral, the other white to upper neutral and I use a wiring nut to cap the red wire and leave it in the junction box.