2 year old pit/lab mix suddenly stopped going outside to poop

Hi all. Made an account to post this. I am having an issue with Zeus, my two year old pit/lab mix (pictured above). He is a very well-behaved dog, and has always been very good about letting me know when he has to go out.

However, about a month ago, he suddenly started crapping in my house. He gives no indication that he needs to go, and simply wanders into another room and does it on the floor. He does not pee in the house, only poop. It's as if he has decided that he no longer has to go outside to do it. He has no interest in doing it outside, in fact he seems to hold it until we come back inside. Even if I take him out every 20 minutes, he refuses to do it until we are in the house. Often times I will take him for a good long walk, and he wont crap once. But then 20 minutes after getting home, he does it on the floor. He still asks to go out if he has to pee, but pooping seems to be an indoor thing now.

Nothing has changed in his life or mine, my schedule is the same, NOTHING has been changed, so I can't figure out what is bringing this on.

He is 2, no health issues, no allergies, no behavioral problems besides the recent pooping thing.

Any advice/ideas would be appreciated.

What do you do when he does this? Do you get cross ??