I had this happen, too. My tank just received its first coral and the "peppermint shrimp" started to pick at it in the evening. Only it, though. I introduced three frags: a micromussa, a maze brain, and a toadstool. I shooed them away dismissing them as curious. By the morning, however, the micromussa was devoured. It is possible that it is completely retracted, but I doubt it given how vibrant and healthy the others look.
I was surprised. The "peppermint shrimp" always seemed to keep to their cave and eat algae, left-overs, seaweed, etc. Also, my LFS insisted they were reef safe. But I failed to ask which they were. There are two primarily sold as "peppermint shrimp" one of which is "definitely" not the reef safe while the other much more so (though experiences vary).
Lysmata Boggessi aka Atlantic Peppermint Shrimp = NOT SAFE
Lysmata Wurdemanni = REEF SAFE (mostly)
Apparently, misidentification is common even for LFS and even in spite of some clear markings.
So, my question to this forum was going to be "what type of corals might be safe from the 'peppermint shrimp' I now appear to keep (lysmata boggessi)?"
But it is sounding like its possible none-are, and it just depends on whether they need to scavenge around or not.
My toadstool appears unharmed or uninteresting to them as is the maze brain.