I agree with what RVhiker has said.
I would add, the loose/dirty receptacle in the pedestal has more electrical resistance than it should, and as your RV draws current through that resistance, there will be a voltage drop develop inside the receptacle. The voltage drop multiplied by the current draw, is the power consumed inside the receptacle. The blackening of the prongs is what you see afterward.
So, even though the CG voltage may be above the EMS cut-off, the extra drop inside a loose/dirty receptacle could be just enough to trip your EMS.
If you want to boost the CG voltage a bit, you can use an Auto-transformer, as found in this link to Tweetys;
You install it between the pedestal and your EMS.
Be advised, some CG management frown upon using an Auto-transformer, but from a technical standpoint, it will NOT do any harm to their systems.
P.S. The best solution is to have clean tight connections in the receptacle and tight screw terminals where the internal wires connect to the receptacle. I've seen cases where the receptacle is okay, but the internal screw terminals for the wires are loose, resulting in excessive voltage drop.