WooCommerce POS changed the way products are downloaded in version 3.1. Orphaned products may still exist in your database but they should no longer cause a problem with WooCommerce POS. This post has been moved from the FAQ to the blog.
One of the most common causes of problems with WooCommerce POS is ‘orphaned variations’. An orphaned variation means there is a variation product in your database without a parent variable product. The product cannot be seen on your site or in your admin screen, but it exists in your database and can cause problems with some plugins, including WooCommerce POS.
Orphaned Variations in WooCommerce
Orphaned variations seems to have been a problem with earlier versions of WooCommerce (pre-2.0). Because they do not show on the product page or the admin screen they can sit undetected for many months without causing a problem.
If you are seeing orphaned variations you should clean up your database using the button provided. If you prefer a more hands-on approach you can examine the database yourself using something like phpMyAdmin. By using the snippets below you can manually search and delete orphaned variations (thanks to Patrick Garman).
https://gist.github.com/pmgarman/6135967