Posting our failures is vital to learning. Just when I think I have it figured out something happens. I'll occasionally have a coral STN while others are fine. Of course it's usually one that I like most.
It may, or not, have had anything to do with silicate dosage. I know there is some science regarding the relationship between such and diatoms, but personally in my take the goal is zero. I manage undesirable algae in other ways.
Sorry for the loss, if had that coral I would gladly share the genome.