[haleycookie]

A food switch should be slow and graduate over the course of a week or two for best results.
Maybe the Iams just has an ingredient that Your dogs can’t stomach. All foods mentioned are of lower quality as well. I also wouldn’t suggest switching hard again to the third food. You may see the same issue. Hopefully not. If they like it and do well on it I’d stick with it. It’s the highest quality food you mentioned.