Could it be that you have another consumer on that queue that consumes the messages before you get them in your app? Check the queue metrics, specifically, NumberOfMessagesSent. This will let you know if any messages were added to the queue.
Are you seeing an error messages or is your code throwing exceptions when you are sending messages? Have the IAM permissions changed so that you (and/or the code/Lambda function) are no longer allowed to send messages to the queue?
It looks like you're doing all the right steps. If it were me, I'd delete and recreate the queue as well.
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