Good but incompatible with Mailchimp for Woocommerce plugin

answered by Mailchimp support:

This specific plugin is not supported by the Mailchimp for WooCommerce integration and is not compatible with the official WooCommerce plugin.  That being said, the developer requested to deactivate the Sequential order plugin then test to see if the problem still persists.

The developer was also reviewing the Sequential order plugin documentation and suggested a possible solution that has not been tested but is still a helpful option.

The documentation states: 

Note: If you like to make any of your other plugins (invoice/payment/shipment) compatible with the Sequential Order Numbers for WooCommerce, please make the below tweak.

Instead of referencing $order->id or $order->get_id() when fetching order data, use $order->get_order_number()