If you upgraded recently Windows keeps files that allow it to downgrade to the old version, you can check by going to Disk Clean-up then select the UAC protected option in there and it might have some upgrade files you can delete.

Aside from that I think you just have to give it some time.

There's been a couple of forced re-enrollments into the Insider Build rings with each of the big "service pack" updates like 10586. Try triple checking that under Advanced it does still show "Fast Ring"?

It's not an instant thing. They roll it out gradually.