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I know this is a really old comment, but to answer the question "Why would you ever use ingress queues?"
One reason to use ingress queues is if your backplane is oversubscribed such as on the Cat-6880.
Is this on a ASA with firepower? Are you set to monitor-only in the ASA policy-map? If so sourcefire will mark that they would drop an event, but there would be not actual drop.