If an Orion alert is raised, Alert Central will check to see if an alert already exists that is open. If there is an open alert in Alert Central for the Orion alert, it will add a history record to the alert and will not create a new one. If there is not an open alert, it will create a new one.
In this case, I think the problem is that you are closing the alert or have group policy rules set to auto-close the alert if nobody acknowledges it.
