Something is either stinging it or really bothering it. Those look like necrotic areas. Can treat with some iodine. Do you have the ability to remove the leather for a dip? If do, I would put into a container and dip in iodine for 5 minutes or so. Just help heal a bit because bacteria is a concern now. If not, make up a concentrated dose and turn flow off. Then try to get the iodine directly on the coral on those spots. Should not effect other corals if you are careful.