He’s going through puberty and he is still hormonal. You will need to retrain him.

Yep, he probably hadn’t even reached the peak of his terrible teens when you wisely got him neutered. It takes a full month, and many have observed increased bad behavior just before the hormones finally settle down. (Like men who have a mid-life crisis before they just nap all day.) Seriously, he should calm down in another two weeks or so, and then you can remind him about how to use the litter pan again. For now, put all poos back into the pan, put a bit of hay in there to make it tempting to use it, and hang in there.

my bunny is going throught the same thing. Luckily he’s very picky about where he would pee and pooing outside isn’t quite as bad as peeing.
So i would suggest get him a bigger litter tray. that’s what i did, and i basically puts whatever oops he made outside back in his litter tray. it works great, he now like to go there more often

Exactly what do you mean when you say he isn’t as personable and happy as he was before?

A neuter is still a surgical procedure, and things can take a turn that require medical attention. If he has a change in behavior, like incontinence, he may have a bit of a post-neuter problem going on that needs looking at. You might want to bring him in for a follow-up exam just to make sure all is well, and there isn’t a small infection or a stitch that was missed or something. Rabbits give very subtle symptoms when they don’t feel well, so it’s easy to miss.

But really, if it is the hormones, you will find that patience is the only answer. He has had a surgery (and no one bounces back right away from that, even weeks later) which has altered his body chemistry that directly effects all of his behaviors. As a baby, you only get a glimpse of what his “normal” behavior, his personality, really is. He will change with or without a neuter. You want to be able to differentiate between a negative effect from the neuter and just his changes due to growing up. Baby bunnies will snuggle and binky, but adults do that much, much less. It doesn’t mean they are unhappy however.