Welcome to the Community, @Bradleycooper, and thanks for sharing the detailed report.
From what you've described, this doesn't sound like a local issue. The Agent mode availability is currently being investigated, although we don't have a timeline to share yet.
For now, the workaround is to invoke it with @agent in your prompt. If you're using the ChatGPT app, also make sure it's up to date. If it is and you're still seeing the same behavior, try reinstalling the app.
We've also shared the feedback about the advanced model feeling slower, along with the freezing and cut off responses, with the team.
If anyone else is seeing the same behavior, feel free to add your experience here.
-Mark G.