I don’t have experience with these particular corals but I have a number of others and I will bump your post to hopefully get more traffic.
It looks like tissue retraction to me more than being eaten. In order for anyone to help you though let us know the following.
Water parameters (everything you can test) calcium and alkalinity
What lighting you have
Other corals in tank
Time coral has been in the tank
Age of tank
Stocking list including inverts.
Appreciate it.
Tank is 4-5 years old
Salinity 34.6, but I'm skeptical of the Hanna salinity meter. Either way, that's the consistent reading.
Waterbox reef salt mix
RODI water
Ph 8.1
Alk 7.9
Ca 490
Nitrate 5.3
Phosphate 0.6 (this had dropped to zero last week, but I don't think this is the problem. I would think more of the other corals would show the issue before this one).
I don't have recent mag testing
Lighting is ap700 with (2) t5 supplement. I don't have par readings.
Tank is mixed reef with one bta, with most (not all) of the sps added 4 weeks ago (10 sps frags added 4 weeks ago, all but 2 are going well). The lobo has been in there about 8 months and is pretty much in it's own corner of the tank.
Fish include maroon clown, hippo, yellow tang, and foxface. They've all been in there for years.
Inverts include a lot of bumblebee snails (to combat vermetids), few hermits, Nassarius. I'm probably missing some.
What the FF.
Known for a nip here and there.
Sometimes just a taste, then stops.
I’ve had both FF and a blue hippo taste hammers 5 years after entering the system.