Recurring Error G from a 50A campground pedestal

Experiencing “Error G - possible electrical leakage” on the Pebble charger from a campsite 50A pedestal. It has recurred several times this weekend.

Unplugging everything and trying again resolves the error, but each time I reduced amperage to try to limit recurrence. It works for many hours until the charger shows the flashing red warning. This last time the Pebble was down to 30% SOC before I noticed. Has anyone else seen this regularly?