Alerts like the "Replica set elected a new primary" are considered informational, they trigger an email being sent but the alerts were not recorded in the open and closed alert page in Atlas UI. Also they cannot be retrieved via API.
This is pretty confusing as you'd imagine once the alert is triggered, it'll be recorded in the page where all the other past alerts are kept, the concept of informational alert is vague and never properly communicated to users.
Please record all types of past alerts in the UI and make them accessible via API.