From time to time certain leathers get mucus covered and then shed their skin. they come back with better polyp extension. check your water parameters just to make sure this is whats happeneing.
looking at the pics a bit better, Is that whiteness dead tissue ? or is it a split ?
If it's dead tissue then the leather might be under some sort of stress or dying. If parameters are good and all other corals are doing well then something might be causing harm to the coral.
Also if the leather is in low flow and has a cup shape in the center it could possibly be accumulating detris and waste and if it just sits in the center it could have created the initial wound and further accumulation would further rot the wound more severly. My suggestion in this case would be daily use a turkey baster to blow out the detris and waste from the wound so it doesn't continue to rot away. In that case it should recover, heal back up and be ok.