Do you have any anemonefish with it? My bicinctus would not allow the magnifica to get a single Mysis down. And aside from that, the anemone wasn't really eating well to begin with. It always took a long time for it to react if I put food in it. By now it shows serious signs of atrophy and is so weak that it doesn't even attach anymore.
Like you, I tried all anemones I have (BTA, haddoni, gigantea) and even a couple of soft corals (Xenia & Anthelia) as zooxanthellae donors but nothing worked. I even got a pricey magnifica from Diver's Den and the transfer still failed.