That is a setting. The first time you get refused it offers to stop or switch to 4.8 and if you choose 4.8 it automatically downgrades silently whenever it happens again. I just shut it down and switch to Codex when this happens.

I would also agree that 5.5 feels dumber the past week. More weird logical problems. it's not as dumb as 5.1 or 4.8 but it feels like it regressed.