YES. When not charging BECM reports 3000k which is max value. And if charging with mains ground disconnected it stays the same 3000k. But as soon the mains ground is connected it drops to ~250k.Does that mean "yes", or is it sarcasm?
Charger has already been installed brand newSounds like you may need a new charger.
It's the only component, other than the charge port and cables, that knows about chassis ground.
Maybe disconnect the charge port cables at the charger and test the isolation to verify a charger fault?