Action groups has recently updated the Email notification when using Resource Manager.
In the previous behavior, emails would send only to users who were assigned an RBAC role as a user assignment with an email address configured in their user object profile. Emails in this previous behavior would not have been sent to users who inherit the relevant RBAC role through a group level assignment.
In the new behavior, the users who inherit a role assignment from being a group member will start receiving emails. The emails will be sent to users regardless of role inheritance or direct user assignment, including to users inheriting role assignment through group-level assignment on Azure Lighthouse. This new behavior was rolled out mid May 2024.