Problem:

An ITA notification was sent and instead of notifying one group at a time it immediately notified all members at once.

Root Cause:

Sequencing is not selected in the incident template.

Solution:

Enable Sequencing in the incident template with the following steps:

1. Log in to the Manager Portal.
2. Click the Incidents > Templates. 
3. Click the pencil icon next to the desired incident template.
4. Click Contacts on the left side of the form.
5. Click on the checkbox to enable Sequencing.
6. Click Save.

For more information see Knowledge Base Article 000003646 - How to Customize the Order in Which Contacts Within a Specific Group Receive Notifications in Everbridge Suite