Can't speak to this issue but you could always work around this by getting a Jackery and plugging that into the vehicle and then plugging the cooler into the Jackery. More robust this way, albeit at more expense.
Why not send JEMS007 a conversation request asking him what he found, he has not been on in a couple months but a message sends an alert for me. He never replied to some testing questions like hook it directly to the battery of jeep without the 15' 14 gauge wire run, or add a piece of 14 gauge when hooking to RV. 14 gauge should be ok for a fridge , but I ran 10 gauge to my ARB, and am amazed how fast the temps drop when turning on. He might have had a bad connection in that run which would raiste the resistance of wire.......Jack