PS2 Limitations.
Or something along the line. Basically it does that when the chatlog gets spammed too much, e.g., "Equipment Changed/Cannot Change" too fast, and it creates a bug where it clears the chatlog every time you view log. I had it happen once, but I haven't seen it again yet.
Not sure if Silence actually fixes the issue or just hides the number of Equipment Changed things while still keeping them in memory.
XI Wiki



