@Danhsj I have been dosing Restor, and did an in-tank cipro treatment last week following the guide on Humble Fish, with no change.
I've also recently had an explosion of vermetid snails, which I was made aware of the extent of them when I did a water change, stirred up some detritus, and saw tons of mucus strings. Given the location dependency of torch death, the fact that one of my torches (on the sand bed) has been doing fine, and the fact vermetid snails stinging the bottom of flesh could cause this recession, I'm wondering if that may be the case. I'm doing a dip of my affected rapunzel torch today, and I'm going to try and put it on a frag rack in the tank away from any vermetids.
Related note: I'm pretty sure the answer is "purge your rockwork", but is there any in-tank method to treat (or knock back) vermetid snails? I've been gluing the tips of some, but they keep getting worse.