Your chem is extremely high. I would suggest a few good water changes to bring that back down closer to NSW
levels. High calcium can cause actually cause the flesh to release from the skelaton if maintained over a long period.
The shroom shouldn't be too much a concern but being on the rock is not a good choice. You should really keep these types of corals on the substrate. Hard surfaces/irritants are one of the leading causes of recessions. Also be sure their is no direct or sustained flow towards the moon coral.
The amount of light you have could also be a contributor but that would moreso be shown in terms of bleaching. Basically the flesh becomes white so be sure that is not what your seeing. Brain corals in general do best in med-low HO
reef lighting. In some cases where MH
is used, these types of corals might need a bit of shade.