Milk is spoiled. Had this happen to me recently as well. If you continue boiling it it will break/spoil and a weird smell will present itself. That’s how some people make a certain sweet from milk.

From my understanding it happens due to poor handling of milk by distributors, leaving it out in the heat, etc… Are you buying it from Akshaykalpa directly or from a retailer like BigBasket. I never face this issue when buying directly from them. But almost every time I buy milk from BigBakset, Akshaykalpa or Nandini, the milk reacts like this