Duplicate email issue

Hello,

I identified a duplicate email issue related to the plugin when editing an order or changing its status to “completed” from the WooCommerce admin.

Environment:

• Latest version of WooCommerce
• Latest version of WooCommerce PDF Invoices & Packing Slips
• WP Mail SMTP enabled
• Issue reproduced both locally (MailHog) and in production (Brevo SMTP)

To diagnose the issue accurately, I developed a custom WordPress email debugging plugin that traces wp_mail() calls with full stack traces, hooks, and plugin origin detection.

Issue:
When the order status changes to “completed”, WooCommerce correctly sends the “completed order” email once.

Then, the plugin triggers a second identical email.

The second send appears to originate from:

File:
wp-content/plugins/woocommerce-pdf-invoices-packing-slips/includes/Admin.php

Line:
1563

Method:
send_emails()

Detected trace: 4

wp_mail
woocommerce/includes/emails/class-wc-email.php : 1136 5

send
woocommerce/includes/emails/class-wc-email-customer-completed-order.php : 79 6

trigger
WC_Email_Customer_Completed_Order 7

send_emails
woocommerce-pdf-invoices-packing-slips/includes/Admin.php : 1563

The plugin appears to call:
WC_Email_Customer_Completed_Order->trigger()

even though WooCommerce has already sent this email earlier in the same request.

Result:
Customers receive the same “completed order” email twice.

The issue is consistently reproducible when:

• editing an order from wp-admin
• changing the order status to “completed”

Additional information:

• disabling the plugin immediately removes the duplicate email issue
• the problem occurs even without Brevo (reproduced locally with MailHog)
• WP Mail SMTP is probably not responsible, as it only handles email transport

You may want to check whether send_emails() should ignore WooCommerce transactional emails that were already sent during the same workflow, or prevent a second trigger of WC_Email_Customer_Completed_Order.

Thanks.

mp-weblab