I actually had this problem with Niner when he was on Pro Plan as a puppy and even as an adult. We tried pretty much every ProPlan line. He always had soft poop - always. He did pretty good with PPSSS until they changed the formula a few years ago. I really wanted Niner to be on ProPlan but it just hasn’t worked for us poop wise. My shepherd is on it and she does great. Hope the lamb puppy works well for your pup