When service instance have the same name, it may not show up in a service usage table due to the sorting that is used in the table.
The cause of this issue is the way the data is sorted and presented in the UI. The service usage table is grouping by service_guid, then displayed in a table under the service_name, then groups all of the service instances by the service_instance_name, and then shows the total duration_in_seconds of all the service instances in the row. service_plan is not considered when creating the table. It arbitrarily picks a service name to display in a Plan name column. Therefore when there are multiple service_instances with the same name it may not show up in the table.
The sorting/filtering logic is fixed in Apps Manager v677.0.56+