I checked in with the team about this, and they’ve confirmed this is a known issue. The newer Google preview models (Gemini 3 Pro and 3.1) can have reliability issues at the moment, which can make them seem unavailable even when you haven’t used them much.
The team is actively working on improving this by increasing capacity and reliability. In the meantime, you should have better results using Gemini 2.5 Flash, which is more stable right now. You can change it via the model picker dropdown.
Hope this helps, let me know if you have any further questions!