Reported the same issue about 6 months ago, CW could not duplicate the issue in the shop. during our 41 day trip to Oregon it happened three times but never filled the tank full but if I did not check levels every day I'm sure it would have.
I have started to systematically try different ways to make it happen by turning on the pump when I'm hooked up to shore, trying to remove pressure from internal system before hooking up shore water. CW did say it could be the pump check valve and if it happens again I'll have them change out the pump before warranty ends.
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