I think this is the most likely scenario for a burned up cord with no (or late) breaker trip.
Corrosion at the wall socket of the camper.
A corroded, pitted connection can increase resistance (and thus current demand) at the socket that the 30 amp breaker inside the coach does not "see" (so it will not trip and end the high resistance short at the socket).
Temperature at the bad connection will increase at the wires until something gives (the wires, the socket, or the 50 amp breaker).
Lou, Laura, & Freya the wonder dog
2008 GMC Sierra 3000HD Crewcab SB Allison Duramax
2019 Flagstaff 8529FLS - Pullrite 3300
HAM CALLSIGN - KC3FFW