Welcome to AA!!! In order to help figure it out, please post the following info:
Could be a number of things. Fish could be nipping at it, Not enough light, Inverts could be harassing it, water quality issues, neighbor corals could be stinging it or it just may be acting like an LPS
My Frogspawn, Hammer, Trumpet, Open Brain corals all go through periods where they only inflate a little or not at all. Try giving it a few days.
Do you add any chemicals to the tank? (ie. Buffers or Supplements)
What do you feed the tank? (Frozen, Flake or Pellet)
What kind of Salt Mix do you use? Do you let it sit for 24hrs with a powerhead and heater to airate and mix fully?
Do you use RO
water? How do you Top Off evaporate?