Coolant overflowing the overflow container.

GordonThree wrote:
So it's repeatedly overflowing, but you're not adding coolant? How is that possible?

He said it's wet, not making a puddle.
It's unfortunate that car dealers won't stand behind their product and actually take on a perceived difficult to diagnose situation, but that's about the $ and car dealers have way less interest in sinking some of their $ into diagnosis than they do having you "trade it in."

Idk how you'd pressure test the system, but if the cooling system is holding the required pressure then I'd be looking for an internal leak i.e.: head gasket.
But the fact that it's coming out around the cap vs the overflow leads me to believe there's a small flaw in the plastic tank neck not allowing full pressure to build and that it would be more prevalent if you were working it hard.
I've seen what I just described more than once. Mostly in motorsports applications, bikes, snowmachines etc. there are actually fixes offered for some of these applications where a particular model is the issue. Like coolant reservoir sleeves that prevent distortion of the tank neck.

Back to the head gasket. If that was the case, I would expect coolant to be expelled through the overflow, not the cap.
And it can be very small. Wife's car had been "eating" or leaking a small amount of coolant for years. Maybe half a quart or quart every 5-10kmiles. No evidence of external leak, no evidence of internal leak (water in oil, oil in cooling system, washed out spark plugs, etc). Finally after like 5 years, the minuscule "hole" in the plastic radiator end cap started leaking enough to diagnose. Prior to that, it must have been puking a few drops under high heat, load conditions and hitting the road and leaving no streaks, stains, drips on the chassis.
My money is on the tank where the cap screws on.
Quick test would be to see if you can seal that cap up solid. Not sure if it's a pressure relief cap to the overflow or simply a fill point that is not designed to release under pressure. Some thread tape, if it's a threaded cap or something similar. Then go for a drive and see if the drips are present.