Wrong order content in confirmation email under load

Hello VillaTheme Support,

We are using WooCommerce Email Template Customizer Premium v1.2.12 on our store.

During a recent traffic spike, we had a serious incident:

Customer of order #106774 received a confirmation email addressed to their correct email, but the content was from order #106769 (order ID, name, address all mismatched).

We investigated and found:

Action Scheduler shows no duplicate or failed jobs → queue is not the cause.

VIWEC logs show multiple renderings for both orders within minutes:

Order 106769: rendered twice at 14:06:57–14:07:04 (new_order, ES).

Order 106774: rendered three times at 14:09:33–14:09:42 (completed/new_order, EN).

This suggests a race condition during rendering. Looking at the source code, the Email_Render class uses a singleton and keeps the email HTML in a property ($this->mail_content_html) until injected via woocommerce_mail_content. If multiple emails are processed in the same request, the buffer can be reused between orders.

We need your guidance on:

Does the plugin use global state (singleton, shared buffer) for rendering, and could this cause cross-order contamination under concurrency?

Is there a way to force per-order isolated rendering (e.g. always instantiate a new Email_Render)?

Can we safely disable all caching/state in VIWEC, or apply a patch to ensure $this->mail_content_html is reset and the filter removed after each send?

Have you encountered similar reports, and is there an official fix or update?

This is a data protection incident for us, so we need urgent advice to ensure no further customer data mix-ups.

Thank you for your prompt support.

Best regards,
EI