This exact situation happened to me. I have an 8 head torch which was doing well....until...my clowns tried to host it. (can't be 100% this was the cause, but suspected.)
The Torch started to expel its zooanthelle ("brown wispy gunk") until all of the heads looked miserable.... bordering on dead.
I researched the issue and persisted with the coral. I am happy to report that several months later the coral has started to come back.
I have 2 of the 8 heads back, and the others are showing signs of recovery.
Do not be surprised if something similar occurs, and do not assume all is lost prematurely.
I read it can take up to a year for the coral to fully recover.
Hope it helps. Good Luck