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 paid company Google Workspace account is stuck on 3.6.

My free gmail account is not.