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?
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.
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
What is your reason to believe this is not a bug specific to a small set of Pro users?