Light spot at the top

Hello everyone!

I noticed a light green spot(s) a few days ago on one of my three Bolivian Torch seedlings. The only change has been repotting it into a 4-inch terra cotta pot, 4 weeks ago (all three had a repot). The soil is the usual mix of 60% perlite and 40% MG cactus mix, and a sprinkle of Earthworm castings. I withheld watering for a week after repotting and have been watering every 1 to 1.5 weeks, depending on how light the pot feels.

I’ve also been gradually increasing sun exposure. It has always been outdoors facing southeast under a roof for months, as I live in Florida it’s gets indirect sun all day then about 4 PM it gets direct sun until dusk. When I remember, about 2-3 times a week, I bring it out to receive additional morning sun until around 11 AM.

The only possibility I can think of is sunscalding, but the other three plants are fine.

Any thoughts or theories?

EDIT: it’s not soft or mushy when I touch it.