Lots of good advice above! Possibility of loss of neutral is high. Once this has happened, any appliance connected at the time may have serious damage even if somehow neutral was restored. Lightning can cause the same or worse damage.
Low voltage on one leg of a 50 amp service is often accompanied by high voltage on the other leg. The situation can disappear and re-appear as different appliances are connected and disconnected. This mysterious and confusing effect is a symptom of lost neutral.
It can be specially confusing if you are not expecting the voltage to change and you rely on the reading you took under a different loading condition.
https://www.dutchmen.com/resources/m...erter_info.pdf
Sparking and smoke can have multiple causes. Loss of neutral or lightning can cause sparking and smoke. Remove 120 volt power from the system.
Open service entrance covers and inspect wiring inside. Burned insulation, eroded, and corroded wires need correcting.
Remove 12 volt supply. Open converter/charger cover inspect wiring inside. Burned insulation, eroded, and corroded wires need correcting.
Even if the above are corrected, the converter/charger may still be compromised. Components inside may be toast.
Continue tracing both hot legs and neutral wire from main breaker all the way to the pedestal. Inspect for damage. Pay special attention to any connections or contact points. Plug blades, sockets, and contactors on cord reels are weak points.
There should be no connection between system ground and the neutral wire in the RV until the RV is connected to shore power. It can often be difficult to find find these ground faults, especially the ones between neutral and ground. Hot to ground faults often show up as sparks, smoke, or tripped breakers.
Appliances damage by high voltage when neutral is lost or lightning strikes often develop ground faults or worse.
Note: Loss of neutral in the pedestal, campground system, or local grid can cause all these problems. You may not know if or when the loss was corrected.
I wish you good luck and happy trails ahead!