Hi,
Did you do your water tests? If water quality is off, some corals are more sensitive then others and show stress faster...although elegance corals generally like the dirtier water...maybe it's too clean. The leathers often look like they are dying but they are shedding their "skin" and that's why they need a good water flow, to help them sloth it off.
That last picture looks pretty bad.... do some water tests and give us the numbers. whatever you do, don't just start dosing stuff like calcium, do the test first to figure out what exactly is needed.