I've been running Sequoia 15.1 since it was released. I soon thereafter was taken off the waitlist and had been using Apple Intelligence until this morning.
My first hint something was wrong was that Writing Tools, which I'd been using extensively, disappeared. I tried in another app, and it wasn't there, either.
I then looked at the Siri icon in my menu bar - which looks different under Apple Intelligence - and it had been reverted to the old icon.
I then checked my Apple Intelligence settings and, sure enough, not only was it off, but I'd been returned to the waitlist.
My iOS and iPadOS devices continue working just fine with Apple Intelligence. Only my MacBook Pro is experiencing this issue.
Has anyone else seen this?