I see multiple endpoints with the same hostname on the Endpoints page.
Use filtering to search by hostname on the Endpoints page to identify all endpoints with the same host name.
Locate the endpoint with the most recent time in using the Last Checkin column. Check the box to the left of any endpoints with older check in times and check the box to the left of the hostname. Click the Decommission button that appears to confirm selection.
The most common cause is the sensor being uninstalled and reinstalled on an endpoint which will trigger a new sensor ID to be assigned to a particular endpoint.