I think you will get more hits if this stays in the reef forum as is.
One suggestion that I have is to be on the look out for possible preditors.
Check the stalk in the morning and at night for tiny bugs that may be climing your leather, also a white nudibranch, possible that it may be some type of preditory snails as well.
If truly damaged then it could also be releasing more chemicals than normal I suggest running some fresh carbon.
NM - I've not heard of leathers dropping "plugs" so to speak, I'd be interested to learn more if you know anything else about it. :thinking: Or did you mean a section like on the outside of the coral
Thomas