What is going on here

[ghill]

And how do I fix it?

 

[Timfish]

Tissue is receding. It may be too close to the scolly or it may be too much light. While I try to avoid moving corals as it's a source of additional stress as it will have to adjust it's photobiology to a new location this situation requires it. As the tissue farther away from the scolly and in lower light looks better I would move it downward a little bit.