Why certain line items are not added to bill when converting multiple purchase orders to bill from purchase order list page?

This occurs when the missing line items are included in a purchase receive. In such cases, you can create the bill directly from the purchase receives. To convert a purchase receive into a bill:

• Go to Purchases on the left sidebar.
• Click Purchase Orders from the Modules bar and select Purchase Orders.
• Select the preferred purchase order.
• In the purchase order’s details page, go to the Receives section.
• Click the required receive.
• Click Convert to Bill on the right corner of the receive.
• A new page will open along with all the details automatically fetched from the receives.
• Enter the necessary details and click Save.

Your purchase receives is now converted into a bill.