If you see an extra or unknown line item on a quote you generated, it is because you have an unbilled charge that is yet to be posted for the subscription and is being included in the quote, this is noticed when you have the "Detailed Breakdown view" configured. 

Also, see the consolidated view.

Note: This applies only to existing subscriptions that are being changed.

Related articles and Documentation

How to view the details of changes to the unbilled charges via the API?

Charge /Invoice one-time fee in Chargebee