Intermittent coolant leak?

My son is driving our 2015 Cruze with 118K miles back and forth from Kansas City to Lincoln Nebraska. On his way back to Kansas he had the "turn off AC message" come on going up and down some hills. The temp gauge went slightly above the middle. At home he took the car to work and noticed the heat was working, then not working. He's not mechanical (is an electrical engineer but never worked on cars). I explained to him how to check and add anti freeze, which he did and it helped. Because we saw a puddle under the front of the car when he was adding coolant, we both figured it had a leak that needed attention soon. So he drove the car all the way back home last night, some 250 miles and this morning I looked at it and I see nothing! Nothing on the ground as far as a leak and the coolant reservoir is full! I'll look at it again but I hate problems where you want to fix something but it's not apparent where it's broke. Wondering if anyone else has had this problem or any insight. As a side note I had at least two issues with my 2005 Trailblazer that's been a really good vehicle and both issues seemed to magically go away and I've not had them happen in years and it has 265K miles on it now. So I do realize that some problems can indeed come and go. I'm thinking about taking the car to the dealership for it's first 4 wheel alignment anyway so maybe I could just let them take a look at it I figure.... Maybe they could do one of those fluorescent dye checks and put the system under pressure.