He's completely normal. Has done this for about a year. Multiple costly vet visits for them to say "What have no fucking clue". I think he just likes leaving me presents to come home to at this point.
Otherwise normal cats who go outside of their litter box are usually upset about something in their environment. Are the boxes near something noisy or surprising? Are they in a private spot where he's not going to get approached while he's using them?
If there's a regular spot where he goes, maybe try putting a box on that exact spot. We had a similar problem a few months ago, where our cat was peeing in the basement on a stack of paper he found. We moved everything away from that spot and put a box there and now he's happy as a clam.
