I have experienced similar things with my sps though not quite as severe. Some pods in my tank build little mucus tubes to hide in and cover them with detritus. These occasionally occur in corallites in the middle of sps. They do the same thing and chew at the edge of healthy tissue preventing their holes from being covered up. The pods I have seen do this are smaller, white, and cigar shaped for living inside a linear tube. The will also grab bits of detritus like chaeto strands to adhere to their tubes which further inhibits growth. IME interceptor does not knock back their population much. I imagine they are somewhat shielded by living inside the tubes. Wrasses are not a great solution again due to their concealment in the tubes. I havent tried mandarins yet, they might scrutinize the rockwork more and do a better job of control.
Good luck. Let me know if you find a solution. I would definitely address that Acro asap, with vinegar, superglue, or boiling water injections.