Here is a couple of experience I had with nems, just my personal experience, my journey from not being able to keep a BTA alive to now where I have pretty much every commercially available anemone species at this point. Maybe you can gleam something useful from it.
1. The first 6 years of keeping a reef tank i had a really hard time keeping any anemones alive, tried 6 times died within a couple of weeks every single dang time. Every time they settle in looks good for a couple of days, ate some frozen silverside, then in a couple of weeks they just wither away and died. The only anemone I managed to keep alive was a rock flower anemone. Until one day, I fed my rock silverside, which I only fed to my BTA so far, within a couple of days, my massive rock flower, started to die, his stomach flipped and he died. Thats why I dont ever buy silverside anymore.
2. I had a biocube for 3 years, where every single anemone I put inside wither and dies, always thought it was the water or something, but one day, when i tore down the tank. Moved the rocks to my clown fish tank with a couple of BTA that I had for years. Within a couple of weeks they all died. Im pretty sure it was due to some bacteria that present in the tank and when i transferred it to the clown tank the bacteria or whatever pathogen traveled with the rock to the tank killing all anemones. I cleaned up everything cure the rocks qt the fish and once again anemones no problem.
3. This applies especially to wild caught anemones especially from less reputable sources, like petco and stuff. I use to have a maybe 50/50 survival rate with anemones from petco, until I tried the antibiotic treatment method, seriously its a life saver. I have a carpet nem that looked like mush comeback to life with ciproflaxin. Once thing that I have noticed as well is that when an anemone is infected necrosis happens in the stomach and the foot first.
4. Just a side note, when i buy nems, the thing that I always ask is is the tentacle sticky and if the foot is attached, I have never lost a nem that is doing both.
Also just my input in my experience an anemones that is starving, slowly shrink and when I say slow I do mean slow, and the first that goes is the tentacles, it gets shorter and shorter. Stomach should never protrude if its starving, they start to look like a dish. I had a sebea that got covered by a monti once, and it took him like 2 months + without feeding to shrink.