Rain water in spare tire compartment

A few months ago, my wife had a flat in the rain. After she got home, I was getting the flat tire out of the spare tire well and noticed about 2 inches of water. Thinking that the flat tire may have filled with water until she got the car stopped, I just dried it out and forgot about it. About 2 months later I was checking tire pressures and noticed about an inch of water in the spare tire well. Took the 2018 Traverse to Chev. They could not find any source for the water so I brought the car home. About a month later after a medium rain, I checked again and lo and behold, water in the spare tire well again. Back to Chev. but once again they could not find a problem and they even left the car outside during a 2" rainfall, sitting level the same as my driveway.

I am puzzled as to where the water might be coming in and how to determine the problem. No idea why the car did not leak for Chev dealer. They even sent me videos when they opened the well to show, no water.

Anyone else run into this?