Bug report: customer_on_hold_order uses stale template and does not send correctly

Hello,

we found a reproducible issue in WooCommerce Email Template Customizer on our site.

When WooCommerce creates a bank-transfer order and changes it from pending to on-hold, WooCommerce correctly triggers the customer_on_hold_order email. However, your plugin appears to reuse stale renderer state from the previous email in the same request.

What we found:
– WooCommerce does trigger customer_on_hold_order normally.
– Your plugin correctly selects the customer_on_hold_order template.
– But during rendering, it uses the previous template instead, typically the admin new_order template.
– As a result, the customer on-hold email is not sent/logged correctly for some orders.

Technical detail:
– In includes/email-trigger.php, the plugin calls Email_Render::init([ ‘template_id’ => $this->template_id ]).
– In includes/email-render.php, Email_Render is implemented as a singleton.
– Because the singleton is reused, template_id is only set on first construction and is not refreshed for the next email in the same request.
– This causes the second email to render with the wrong template ID.

Example from plugin logs:
– For an affected order, the log shows customer_on_hold_order matched template 10137
– But immediately after that, render logs show render – template_id : 9525
– Template 9525 is the admin new_order template, not the customer on-hold template

Impact:
– On-hold bank-transfer customers may not receive the email with payment/bank details
– Admin new-order email can still be sent, so the issue is easy to miss

Could you please review this and confirm whether this is a known bug? It looks like the renderer state should be reset or the template_id should be updated for each email render within the same request.

Best regards,
Diana