Hi,

When transferring products with variants between two Odoo databases, Odoo does not automatically preserve the external identifiers (`xml_id`) for product variants (`product.product`), even though they are essential because all transactional records—like stock moves, sales, and purchases—reference the product variant model, not the product template. During export, Odoo only includes the business data, not the technical metadata stored in `ir.model.data`, where these external IDs are kept. As a result, when you import the products into another database, new variants are created with new internal and external IDs, breaking references for future data transfers. To fix this, you need to explicitly export and re-import the `ir.model.data` records related to `product.template` and `product.product` or use an XML-based export/import instead of CSV. The XML format automatically retains external IDs in `<record id="...">` tags. Another option is to run a small Python script after import that programmatically restores the same external IDs for each variant. The most reliable process is to first ensure all attributes and values exist with the same external IDs, then import the product templates and variants using XML or by preloading `ir.model.data` entries. This guarantees that both databases share identical external IDs, ensuring future imports—such as stock moves or order lines—can link to the correct product variants without conflicts.

refer:

1.https://www.odoo.com/documentation/19.0/applications/essentials/export_import_data.html

2, https://www.cybrosys.com/blog/how-to-import-product-attributes-and-product-variants-in-odoo-17

Hope it helps.