Kirkland is a diamond product, their consistency is not the greatest, have you swapped out bags? Meaning, during the months he had loose stool was it on the same bag of food or across different bags? usually bags come in lots, now that i think about it, even if you swap out bags they could be in the same lot with the same consistency with each other. i would recommend slowly switching him to a higher quality kibble, i like california natural (p.g. sucks!) since he seems to have a unstable stomach at the moment.