Mine did, too, and I discovered (by pure luck) a rather bristly bristleworm in the same hole as the mushroom. I got the worm out (or, at least half of it) and now the shroom seems to be coming back a bit ... slowly. Could something be irritating yours?
standard 55 lbs LR
, 60 lb live sand, 10 gal
sump/refugium. Urchin skimmer, mag7 pump, 3 x 96W PC
combination 10,000K/actinic bulb, 2 blue LED moonlights
1.024, temp 79.5, pH 8.4
Livestock I added:
1 skunk cleaner. 12 hermits: red, scarlet, blue. 15 or so assorted snails. Discosomas, Ricordia, Rhodactis mushroom corals, chaetomorpha (sump), 1 feather duster, Montipora digitata
, Montipora capricornis, Montipora hispids.
assorted zoos, Xenia, Kenya tree coral, green Sinularia, green star polyps, branching hammer coral, bubble coral, Devil's hand leather. Yellow chromis, purple firefish.
Hitchhikers: the usual suspects :crabs, bristles, urchin, mantis shrimp (now in exile in mantis tank)
List of possible/likely newcomers:
Feather duster. PJ cardinal, Bangghai cardinal, Firefish goby, Clownfish, Neon goby, Yellow watchman goby, Orchid dottyback. Various corals.