The interesting thing is that when I look on the FTP server, in the attachment folder (/wp-content/uploads/wpo_wcpdf/attachments) I see a mix of correct (39kb) and incorrect (214kb) invoices being sent out: https://imgur.com/a/qElQdDa
The site is just a regular wordpress installation and does rely on WPML (3.9.4), WPML String Translation (2.7.3), WPML Translation Management (2.5.2) and a bunch of other WPML related plugins: https://imgur.com/a/b8eXpRt
Do you think it might have to do with memory issues? When I look at the status page of your plugin it is complaining about memory limits. I can look into the hosting settings if that might affect it: https://imgur.com/a/ZZfJB6N
