I see what's happening. When you reset the invoice status to draft and add more line items, Odoo should defintely reflect those changes in the PDF invoice. I've run into this issue before, and it's often due to a caching problem. Odoo sometimes caches the PDF, especially if you're using any custom templates or modles, which can prevent new data from appearing immediately.

First, try clearing the cache and check again. You can do this by restarting the Odoo server, which forces it to generate the PDF fro scratch. If taht doesn't work, look into the PDF template. Sometimes, the template might not be updated to accommodate new line items correctly. Make sure the report template is using the right variables for line items.

If you've customized the invoice generation process or use a third-party module, make sure they're compatible with Odoo's base functionalities. Third-party apps or customizations might not always be fully compatible with core updates.

Also, check the logs for any error messages when generating the PDF. They could offer clues if there's a bigger issue at play. If you're stuck, talk it over on the Odoo community forums or reach out to a consultant. Sometimes these issues need an expert eye to spot what's going wrong.