dog won’t stop pooping inside

Hello all!

I have a 1 y/o cattle dog who is an absolute dream. He is well behaved, listens keenly, gets hours of exercise, and sleeps a lot of the day. He's a pretty happy puppy. We never had issues with peeing inside, and he potty trains well, but he won't stop popping inside. We've tried everything. Training, vet visits, better positive reinforcement during walks, he's crate trained, he is fed on a specific schedule, everything. Sometimes he goes weeks without doing it and then he suddenly does it for a week straight. He goes on three 20-30 minute walks a day, will poop, walk back toward home, and then poop inside. Nobody is sure why or how to stop it. I'm not either. If you have any ideas I am all ears. Thank you!