i don't do chocolate milk, but that label explains most people's milk issues. for years i couldn't figure out why i couldn't drink a whole glass milk without causing problem, but had no problem with cheese, ice cream and other dairy products. then i learned about the the difference between the A1 and A2 protein from the different cows. jersey cows have the a2 protein and doesn't cause me any problems. that's why even though i mainly use the nut milks (cashew is my favorite), when i'm in the mood for some cow's milk it has to be an A2 variety.
so for me and alot people who thought they had an issue with the milk, it's not the milk it's the protein.
https://www.ericksonliving.com/tribune/artiles/2017/08/what-a2-milk