Have you added other corals to your tank? Could be chemical warfare.
"Water parameters are good" is subjective. Can you list the values of the various parameters you tested?
I had these two varieties for several years and then they slowly melted away. The pink ones are long gone, a few blue ones are still around. It could have been too much competition for food, chemical attack by other more aggressive corals/mushrooms/etc. I never pinned it down. Other mushrooms thrive but they are "bumpier", not smooth like these. The blue ones actually began to take over my tank for a while. The pink ones always preferred low light, low flow. Perhaps you have them too high in your tank. Try moving them under a rock shelf.
They are not multiplying, they are not healthy. I believe these multiply by pedal laceration whereby you will see young ones appear near the base of larger ones. I never saw them actually split like larger hairy mushrooms.