Emails I got today:
Your Prepaid REDcard® Account has been locked because we found activity that violated section 15 D of our Prepaid REDcard User Agreement.
Seriously?
And they better give my money back.
You will get your money.
As to the closing of your Redbird account by Amex, it has happened before a couple/few times, for instance
back in May someone reported a Redbird shutdown with the same 15D verbiage on Reddit and people started to freak out thinking Amex would close Redbird accts en masse.
There's been a couple more such reports that I've seen on Reddit and Flyertalk, including one like yourself (if I remember correctly), after the official Redbird shutdown on Oct 12th. Most likely, the reason for such a closure is the account being eventually flagged for activities done on it some time ago (i.e. not a day or two ago) and once a human on Amex reviewed it, decided to close it proactively.
If I recall correctly, someone on Flyertalk reported having their account frozen, to be closed, and after insisting with the reps on the phone they were able to find out the suspicion was due to the fact that both husband and wife had linked to the same checking acct or something like that, and once they uploaded convincing documents to Amex, they didn't close it. Problem is, Amex normally doesn't tell you why they close your acct in this cases.
All in all, worst case scenario is that you will be banned from any prepaid Amex accounts for some time, but this doesn't happen to all closures... I recall at least one person reporting being able to open a diff prepaid Amex account shortly after a closure. On the other hand, someone who a couple of years ago had their Bluebird acct closed, got a prepaid Redbird from me some months ago, knowing it might now work, it did. This person had tried to open another Bluebird acct after the closure and was denied, then gave up on trying. Their successful Redbird registration was about 2 years after that initial closure, if I recall correctly from the emails (person volunteered the info).