How many polyps has it lost? Have you pulled it, inspected for pests and dipped it? If it's the only coral acting abnormal in the tank I'd start there. Anything near by that could sting it or has fallen into it?
The top one has lost all of them and next one on the right is losing them. but they are losing them uniformed all the way around getting shorter and shorter until they are gone. I have not dipped them yet and these are the only ones doing this.
How many polyps has it lost? Have you pulled it, inspected for pests and dipped it? If it's the only coral acting abnormal in the tank I'd start there. Anything near by that could sting it or has fallen into it?
Check for any pests I had this happen in my tank before and I had those tiny starfish eating my zoas, zoa spiders can be a nuisance too. Id pull the piece and dip it if you can and look closely for pests on there.