Ewout on "[Plugin: WooCommerce PDF Invoices & Packing Slips] Empty invoice-number in PDF"

Hi,
I'm encountering quite a strange problem with this plugin. I have no idea what triggered this behaviour, because as far as i know, no other plugins are updated at the time this problem occurred. I'm using the latest version of this plugin.

The problem is that when an email is sent to the customer or admin, the PDF is attached but has no invoice-number in it's filename or in the PDF itself. When i look in the list of orders, an invoice-number is assigned. When i resend the mail (from the order-page of Woocommerce) the invoice-number displays as it should.

The PDF itself is showing fine, except for the invoice-number.

Do you have any clues / directions?

https://wordpress.org/plugins/woocommerce-pdf-invoices-packing-slips/

Hello Richard,
That's quite strange indeed! It sounds a lot like an issue with server side caching. Are you using any server side caching plugins like W3 Total Cache or WP Super Cache, or does your hosting provider have caching enabled?

Let me know!
Ewout