I would imagine you are experiencing a bug. I've been using 3.8 daily since its release (on a Pro plan in Canada). I believe this is true of many people.
What is your reason to believe this is not a bug specific to a small set of Pro users?
My paid company Google Workspace account is stuck on 3.6.
My free gmail account is not.
I also only have access to 3.6 flash on both my free personal account, and my professional Enterprise account.
Google just takes months to roll out their models to everyone.
My corporate workspace which seem to be a pro account is limited to 3.6 but my personal account at 20/month has given me the latest model always immediately. Flash 3.8 is my go to model for pretty much everything those days
Would that change anything about the conclusion? Having a "bug" that changes available model options for some small set of Pro users 3 months after launch certainly qualifies as a wtf-are-they-even-doing level of bug in my book.