[Delphinus]

Chemical warfare, or more accurately allelopathy, can happen between two anemone species (or even two non-siblings of the same species) but usually it's more of a factor with the colonial anemones (BTA's) against others (other BTA's, or non-BTA species in the same tank - but usually there needs to be several anemones present for it to occur). Ie. once you have a colony of anemones they may act aggressively in the pursuit of territory. There does not need to be physical contact between the anemones.

It's probably not a factor in this case though.

Sometimes a new anemone can wander. They can be stressed for a while and this leads to wandering (even several months after collection). Or there could be a factor such as a tankmate (or hitchhiker) is somehow pestering the anemone. Usually you don't see wanderlust in captive-split BTA's, but its not uncommon in newly imported BTA's. If the attachment point isn't completely to their liking (flow, texture of substrate, lighting, etc.) they may wander. Sometimes they do wander under the rockwork and can't re-emerge on their own and become bleached. This sounds like what you've got happening.

They can recover from this, it will likely take several weeks or even a few months to recover fully, but they can recover. Just try to ensure the attachment point meets BTA requirements, continue feeding, and it should bounce back.

In the case of a BTA, usually the preferred attachment point includes a cave, overhang or crevasse between rocks. They like to move their oral disk and tentacles out into flow and the light, but prefer to keep their pedal disk (the "foot") protected and away from flow and light. They do like their tentacles out in flow but typically not as much as other anemones. Certainly nothing like being near the output of a pump or powerhead, they'll hate that. Getting the right amount of flow is hard to describe. You need some, but not too much, and sometimes experimentation is needed to find the right balance.

The main thing though is that they like to bury the foot into a crevasse or cave, so if you can try to make a spot like that, hopefully it will find it and like it.

Good luck!