I would also appreciate more details. Maybe it was a BA ticket for one of their partners (such as Iberia) that is not also an AS partner?

If it were an error on the part of AS, then I would expect AS to leave your status in place.

I, for one, sometimes do a mileage run at the end of the year based on what has posted to my account. If I think it is in the clear for the status I seek, then I wouldn't do an extra run.

Revoking it months later IF it were their error seems unfair to me.