Same exact issue but mine split, I am new to the hobby and yes I do know (from reading the forum) that I shouldn't have put an anemone in so soon, but I did. I have a 4 clowns fighting over hosting the things. My two guys come out during the daytime cycle of the LED lights (GEMIS 120R) two fixtures over a 120 gal tank, but the disappear into the rock totally at night occasionally coming out then going back in. They haven't eaten (tried pieces of silverside) as of yet. Good color and form. Parameters are good, phosphates a little high 1.0. Temp a steady 77.5
I thought it was normal for anemones to deflate or shrink once in a while as a way of expelling waste. I remember reading that if it happens more than once every couple of days it might be something more serious. It should be fine as long as the mouth is closed and it inflates in a few hours. http://www.karensroseanemones.net/deflating.htm
Are they slightly smaller or completely shrunk down and their mouths exposed.
Anemones cant get stung really by sps, but some lps sweepers and leathers are strong enough.
If the nems have shrunk down and showing their stomach something is wrong. If they are slightly smaller its a process of expelling small amounts over times to keep themselves clean inside. Each night when they lights are off they should do that.
When they completely shrink down something is wrong and they are expelling everything.
One of the anemones is smaller then the other. It seems that the original or at least the one that stayed in the original spot is smaller. Also he has disappeared into the rock totally and I haven't seen him now for a second day. The second anemone is twice his size buy is not as compact, I wouldn't say stringy but he is spread out a bit. I fed him yesterday (half a silverside) and he ate. His mouth is visible but not protruding.
I never feed mine just oyster and roti feast in the tank. Like others have said a picture will help a lot but if I had to guess, it is probably splitting. I have found over the years that RBTA do this in captivity more than any other I have had.