Boy, you're just not having good luck at all.
On the parasitic drain, it could be either the BMS or something internal to one of the cells. Test by disconnecting the BMS and see if the voltage still drops. You could also see if the balancing resistor is getting warm when it's connected.
If your voltage is truly 58.1v on a 13 series pack, you should expect the pack to burst into flames any time now. I hope you have this thing in a safe place where a big fire won't cause massive property damage or loss of life.
58.1 / 13 = 4.47v. This is way above the safe maximum limit. This could happen if you used a charger made for 14s on a 13s pack and the BMS failed to cut off charge. You may still have issues with your voltmeter.
Assuming the pack is fully charged (and then some), but the voltage on both the charge and discharge ports is much lower, I would suspect a bad wire connection or miswire. Even if the BMS is tripped, the body diodes in the FET would pass voltage in one direction. You should be able to discharge through the charge connector (at reduced current) even if the BMS is tripped. I suppose it's possible for the FETs to go bad, but they almost always short when they fail, which would give you output.
Can you post a picture of your BMS? There are a lot of variations on these and it might help to know the general configuration.