Can't really tell from these pics but there appears to be a slime or excess mucus on the side of the fish. If this is accurate, that's usually a sign of something in the water that is irritating the fish's skin. Have you added anything new in the last week or two? ( Fish, plant, fertilizer, decoration, etc)
I would also take a water test of the water at the bottom of the tank. You do this by submerging the test vial with the cap on to the bottom of the tank ( just at the substrate level) then opening the top, filling the vial then replacing the cap and remove from the tank to test. If you are using test strips, take a turkey baster and suck up water from just above the substrate for testing.
You also want to take notice if there is good water circulation at the bottom of the tank.
As for the skin cracking, this could be a few different reasons. One is that the fish is growing so the scutes separate as the new ones grow in. Another is the diet is poor. Cories need a combination of foods including proteins and vegetable matter so if you are only feeding one type of pellet, that could be the issue. You would need to either increase the variety of foods or include a vitamin into the pellets before feeding. But start with the water test at the bottom of the tank.