Cat is dragging his poop outside the litter box?

I have a 4 month old semi longhair kitten. Very happy, very active, loves to eat. Every once in a while, his poop seems to stick to him and he drags on the floor outside his box. It's not diarrhea, it's fairly solid and normal sized. I'm gonna bring it up to the vet on Monday, but I'm wondering if anyone else has had this problem or have an idea what would help? He gets canned food 2x a day (I rotate brands) and a little grain-free kibble. Sometimes he gets store bought treats and sometimes he likes to eat the dog's food. Idk if diet is a factor or if it's his litter or something else?

Sometimes poop just sticks to the long fur back there and gets dragged around the house Keeping the hair around the butt trimmed short will help keep the poop from sticking. You can do this yourself with kid's blunt tip safety scissors and a person to hold the kitten.

Mom's kitty had the same issue. She had a doll faced Persian, pure white and wow, that cat HATED having the 'poop' of shame. We ended up getting the kitty what I called the 'bloomer/butt and belly' brazillian. Not exactly, it was a buzz, but wow, that kitty was SO happy when she didn't have to groom at that fur and the stuff ON it  

Just a side note, if you or anyone in the house has long hair, the cat can end up with your hair in them, and it gets wound around the poop. My two have this from time to time as I have long hair. I've gotten better about making sure they are in areas that are 'hair free' from me, but that's almost impossible