Are you doing a slow and gradual transition by mixing the puppy food and adult food? If not, that is most likely what is causing the digestive upset and the loose stools. Any change in food needs to be done very slowly.
I agree with the other post about the need to transition slowly over a period of a week. Old to New ratios for several days on each: 75/25; 50/50; 25/75
Another thought: the Innova Adult has more calories (504 kcal/cup) than either the Innova Puppy (454 kcal/cup) or Innova Large Breed Puppy (367 kcal/cup).
If you haven't reduced the amount of adult formula you feed, your dog is getting more calories than he is used to. Even eating more than he is used to by 1/4 cup could cause loose stools.