I don't think he was being outcompeted. I have my theories, but will probably never know for sure.So sorry to hear. I suddenly lost my firefish. They are a bit more timid and the other fish outcompeted him for food. I see some good growth on that stylo. Are you able to lower nitrates?
I've been working on lowering them over the past week or so. Planning to test tonight or tomorrow to confirm they're still coming down. The stylo was a mystery frag and I was pretty sure it wouldn't last long, but is honestly one of the best looking things in the tank most of the time.