This incident has been resolved.

Facebook has now resolved this issue, and we're confirming resolution on our end as well. Audiences syncs are back to normal

Facebook has fixed an issue where developers lost access to ad accounts (https://developers.facebook.com/status/issues/470651240279373/). We are seeing audience syncs start succeeding again, and will wait for Facebook to close this issue before resolving

We're investigating an issue impacting certain Personas customers where audiences are failing to sync to Facebook Custom Audiences. This issue looks related to authentication, and we recommend re-authenticating with Facebook while we investigate further.