I had the same issue was because was not getting enough light don’t know if this could be the same for you mine is starting to open up more now I moved it more into the middle but now my toadstool is readjusting there’s always something
Have you checked at night for pests like Asternia, Nudi, Snails? I would lift the piece up and inspect it and give it a good swish with dip in a separate container.
Ca is a little low. What is your Kh and salinity?
It's hard to see the photo. Do you see white dots on your zoas for it to have zoa pox? Zoa don't need bright light. I have them low in the tank