I had a mysterious coolant leak on my 2015 Tahoe. I originally noticed my coolant level in the overflow tank was low, so I would top it off, only to find it was low again a few days later. I never saw coolant on the ground.
After a couple of months I finally started seeing coolant on the floor on the passenger side. After climbing under the Tahoe to take a visual inspection, I noticed coolant on the lower radiator hose. I checked the radiator to see if coolant was possibly leaking from there and traveling along the hose but that didn't appear to be the case. So I decided to replace to the lower coolant hose. The next day, coolant was on the floor in the same location. After further investigation I found the source of the leak. The leak was coming from the overflow tank. I originally thought there was a leak in the overflow tank, but actually it was leaking at the point where the radiator hose connects to the overflow tank. The hose clamp wasn't doing its job. So I purchased the worm gear style camp and installed it. The leak has never returned. I actually put two worm gear clamps on the hose for safe measures.
I believe it was difficult to find the leak in the beginning was because it was a small leak in the beginning and the fluid was only escaping while driving. So the fluid just blew away with the wind, not leaving any trace of a leak other than less fluid in the overflow tank.