A couple of fundamentals:
1. In an electrical circuit, the result of electrical resistance is heat.
2. The heat generation that caused the damage shown in the photos in post #1 will only trip the pedestal circuit breaker if the melting/burning of the plug is so extensive that a short circuit in the plug/inlet interface is created.
3. In my experience the Post #1 damage was caused by high resistance at the plug. This resistance was created in the wire to plug connection or the connection between the shore cord plug and the boat's shore power inlet either because of corrosion in the cord plug or inadequate plug/inlet engagement.
4. The Marinco plugs were designed in the 1930's for use in factories. As such, they were designed to comply with the NEC and carried a continuous use rating of 80% of their capacity.
IMO, it is highly unlikely that loads powered by the panelboard caused a load imbalance between the loads on the L1 leg and the loads on the L2 leg caused the problem. Any imbalance, if it occurred, was created by high resistance in the plug/inlet "system".
At one time I had a five-gallon bucket of burned cable ends and a few burned inlets for boat show viewing. There were no SmartPlug cable ends or inlets in that bucket.
ABYC Master Technician