Marking after big life changes

Hello!

Im just gonna jump right into it.

My husband and I have 4 cats together. We each had 2 when we got married. All the cats have lived together decently for about 3 years now.

Recently my husband and I found out we were pregnant and then bought a house in another state and moved so we could have the baby not at my mom's

My son is 4 months old now. The cats have a bigger space than they did before and generally seem happier. But one of them has started marking things in my son's room. My son doesnt sleep in his room so im kid of confused by this behavior.

The first time it was a toy basket we had gotten from a friend who has a dog so I washed the basket and all of the toys with cat scent deordorizer (nature's miracle brand) and shampooed the carpet with the deodorizer as well.

He marked the same basket again so I repeated all of the washing and carpet shampooing but this time removed the toys and baskets from the room as well as bought a new litter box and set it up in that room. I thought we were in the clear for a few weeks

Then today he marked a squishmallow that has been on the floor unbothered since we moved.

Genuinely at a loss of what to do here so any advice would be appreciated.

Other important information:

He is the only male cat the rest are female, all cats are spayed/neutered, all are exclusively indoor and have been since they were 8 weeks old at least, we have 5 litterboxes available in different rooms throughout the house that get fully dumped and cleaned once a week.