Only thing I can think of is that this particular mushroom is getting too much light. Other heads are looking healthy. The only difference I can see is that the healthy ones are under partial shade.
This is an interesting piece because it also seems to have several sponges (brown, black,etc. ).
Not sure if it's visible or not (I'm on my phone app), but there are some smaller life all over the rock as well. I'll try to retake the image for better ID purposes.
As for the mushroom, should I frag this one and put it under shade? Or if it's partially bleached like this is cutting the head off a bad idea?