For example, if an e-mail notification response rule is triggered manuallyit takes some time to show within the incident that the email has been send.
The Symantec DLP UI does handle response rules by executing them in the background. Response rule actions will be added to a background queue and once the response rule has been executed the incident history will reflect this. However, since the UI goes back to allow you right away the further use of the UI the incident will be only updated once the response rule has been fully executed.
As a result, the observed behaviour is expected and can occur when you experience high CPU usage or a larger queuing. Another resource of delay can be if you have email notification performed via an MTA that has high latency.