I have an 7 year old tabby who up until a couple of months ago has
never had any behavior problems. Now every couple of days he will poop
on the floor and it smells *really* bad and looks like yellow sludge.
He has two litter boxes and they both get cleaned every day. He uses
both boxes and he mostly poops in his box and it looks normal
(although yellow looking). This morning I cleaned out his box and my
cat went to use it right afterwards, but 5 minutes later he crapped
all over a pile of papers I had on the floor.

Also I've noticed that every week or so he will barf up a hairball.
He's never really done that before but they were small so I didn't
really think much of it. But this morning he barfed up a huge one.

Could the two be related somehow? The sludgy pooping on the floor
started a while before the hairballs. Other than those problems he
seems fine. No lethargy or hiding and he's still eating normally. He
never goes outside either.