GPT-5.5 thinking silently routed to 5.4 for 8 days

I manually selected GPT-5.5 thinking, but every response comes back as “used GPT-5.4 thinking” with no way to switch back. This has been going on for 8 days.

I exported my data and found this in the conversation JSON:

• default_model_slug: gpt-5-5-thinking
• resolved_model_slug: gpt-5-4-thinking (every single message)

Can anyone who understands the data export format confirm whether this indicates a backend routing mismatch or A/B test?

I’ve contacted support and they said it would be escalated to a specialist team, but it’s been 4 days with no follow-up.