Hello.

I guess you are asking about Unit serial number tracked items. So if you create Invoice from Sales order you will get a line per item (as it is on Sales order). If you create Invoice from Delivery it will reflect Delivery matrix so you have as many lines on invoice as on delivery (per serial number).

Maybe in your database you have in Sales orders > Settings > Orders setup - checkbox - Invoices based on Delivery = ON. In this case Invoice will be based on delivery no matter how it is created (from Sales orders or Delivery) and in both cases will have as many lines as on Delivery (in this case per serial number).

Regards

Agnieszka