Problem with PDF name after updaten to 7.6

Hey there,After updating to version 7.6, the attached PDFs are no longer named with the default prefix; instead, they have a random sequence of letters and numbers. I've already tried assigning a new prefix, but that didn't work. Do you have any ideas about what else I could try? 

Hi Tobias

Yes, we are using random prefix to avoid direct access to invoice on server which does not support htaccess

However, when the email is sent, the PDF file should not contains any prefix. Maybe on your site there is some kind of override? Please submit a support ticket so that we can check it for you

Regards,

Tuan