Do you have any paperwork for the traction battery replacement? If it were mine, I would discuss the situation with the dealer that did the battery replacement to see if there is any remaining warranty. If not, then I would systematically check all auxiliary systems that use traction battery voltage (heater, heat pump or A/C compressor, onboard charger, and inverter/motor) before going further. There are hazardous voltages involved in all of this testing so I am not advocating DIY unless you are qualified. Unless there are problems in the auxiliary systems, the ground fault is likely inside the battery case or being caused by faulty ground fault sensors.
Silver LEAF 2011 SL rear ended (totaled) by in-attentive driver 1/4/2015 at 50,422 miles
Silver LEAF 2015 SL purchased 2/7/2015; traded 8/10/2019 at 82,436 miles
White LEAF 2019 SL Plus purchased 8/10/2019