There are several possibilities

1. Track Quantity Option are not checked

Track Quantity Option in Shopify

2.Changing data in the Option1 Value, Option2 Value, or Option3 Value columns of the variants

https://help.shopify.com/en/manual/products/import-export/using-csv#product-csv-file-format

Please delete the product link to reconfigure again

You can click the following button to test

1.Detect invalid variants

3.remove old Location

Remove the old Location will break the product synchronization mechanism, please contact us

[email protected]