Duplicate Orders in WooCommerce
The Codisto LINQ WooCommerce plugin is developed to prevent duplication of orders by using a database transaction to commit order data. This approach works 100% reliably when the database supports transactions.
Most Wordpress installations are backed by MySQL databases, which themselves can be backed by different storage engines. Not all of those storage engines are transactional. The MyISAM storage engine is not transactional (see Transaction Commit and Rollback Support MyISAM). As a result it is possible to get inconsistent data because the prevention mechanisms in the plugin are ignored.
If your Wordpress database uses MyISAM, it should be changed to InnoDB, which is transactional. There is a guide at Convert MyISAM to InnoDB which describes how to do this.