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The area of concern to you is known as HLLE (head and lateral line erosion). HLLE which cause pits and flesh missing mainly in tangs, angels and some rabbitfish. It is often caused by poor water quality, high use of carbon, poor water quality (elevated nitrate and ammonia) and inadequate/poor diet. It is not life threating in any way but offers secondary infection in some cases.
As said, if this is on both sides of the fish, it is HLLE or a related condition called epithelial thinning. Also as @MnFish1 said, these lesions are not usually so red. They can get infected by bacteria, or perhaps there is something in the water causing irritation (what is the ammonia level?)