The 50 amp outlet has one leg dead, or the cord(s) have one leg not connected. The 30 amp dogbone connecting both legs points to the outlet having one leg dead. The volt meter testing the outlet as two good legs points to the cord(s) having one leg not connected. The test results are mutually exclusive. (I am assuming that when you say the volt meter says both poles of the "plug" are hot that you really mean both legs of the outlet. If you really mean you tested the plug, it is the outlet that you need to test.)