Amazon sqs messages stuck in available messages

I'm new using Amazon sqs and I'm supporting some queues in my company. The problem that I'm facing is that a few days ago some messages just got stuck in available messages as you can see in the picture. It's not every message that gets stuck.

Do you guys know what this is about?

Solution

I had a similar problem while reading messages from SQS in a recurrent @Scheduled java job. As John Rotenstein pointed out, the deleteMessage method must be called to remove messages from the queue.

In my case, the problem was on the @Scheduled annotated method itself. For some specific reason, it didn't finished executing under some specific conditions and so the scheduler was never ready to run my reading method again.