The elegance coral is one of a few that have a bad long term track record.
While some people report years of success, many find after 3-6 months of great health, it just goes down hill.
Many believe this is an issue of the Indonesian ones versus the Australian ones that seem at least, to fair better.
They don’t require regular feedings and if he’s not taking, it may be a sign of some stress specific to this coral if no one else is affected.
If you have any shrimps, they can damage mouths when they scavenge, so if you have shrimps, they might have made it unhappy. Again, very little the reefer can do.
Long tentacle plates behave exactly the same way, your lucky to get 6-9 months before dying in a week, when everyone else is happy