Each minute when there are no new events available, documents like this are indexed in Elasticsearch.

These are event.original values:

{"messagesDelivered:":[],"queryEndTime":"2023-05-23T19:01:34Z"} {"messagesDelivered:":[],"queryEndTime":"2023-05-23T19:02:34Z"}

This was observed with the other data streams in the integration too.

References

• https://help.proofpoint.com/Threat_Insight_Dashboard/API_Documentation/SIEM_API