Web & Mobile App: Switching to GPT‑5.5 Pro redirects to GPT‑5.3 mini

I am using the $200 plan. After I ask a question using the Pro model, the thinking process ends very quickly, with only a brief flash of “Pro thinking.” And when the model finishes outputting the result, hovering the mouse over the retry button reveals that the model actually responded using GPT-5.3 mini. This only happened when I first upgraded the plan; everything is normal now.