Extreme diarrhoea
The dog loves the food (as part of a 25% mix with other perceived high quality foods) but suffers from flatulence and always has some diarrhoea.
Initially we thought it was something else, until we eventually got around to removing this element from his diet. Over the course of a number of weeks, this has now been removed and reintroduced a few times, with the same results.
Interestingly, he has a similar reaction to the WotW soft acres chicken puppy food a few years ago...