Actually, I’m going to weigh in on the opposite side here, ie. I think he is still in the baby stages and not hormonal, but rather still learning new habits. He’s only 8 weeks old, and it’s even better to start with a bunny who is nine weeks developmentally, so he may just be trying to get it all right in his new home. I would take every stray poo you find and put them all back into the litter box as soon as you spot them. Also, you could put out a second litter pan outside his cage where he likes to roam and poop, so he has the option of not having to find his way back in time to go. Sometimes little ones don’t hold it, and once they poo elsewhere they think that must be OK too. You can teach him to use a litter box no matter what, but you can make it more convenient.
And congrats on having a baby who is great about peeing in the box! That’s not always guaranteed with his age. He sounds adorable!