It could be. You're missing a ground somewhere, so a break in the ground conductor of your cord or adapter could be the culprit. That's easy to check with an ohmmeter (be sure to disconnect from shore or generator power before trying to check this!) Just measure between the power distribution panel (breaker box) ground bus in the RV to the ground terminal of the cord and then the cord plus the adapter.
Bear in mind that, unlike your home panel, the neutral and ground buses in the RV's power distribution panel should NOT be bonded together. The RV's power distribution panel is considered to be a sub-panel when you're connected to shore power, so the single allowable neutral to ground bond is at or upstream of the shore power pedestal at a "main" power distribution panel. If you have a generator in your RV, the neutral to ground bonding is handled in the transfer switch when you're on generator power.
Rusty