XML Bursting file name email attachment shows random characters.

We're using XML Bursting to generate and send the invoice to customers. We've recently implemented this to our Germany customers and it's been working as expected. Recently, we had an issue with one of our Germany customers. We're using customer name + Invoice Number + Term Name as the filename and attaching it to the email to the customer. For some reason, the name of the file attached to the email shows weird characters when the customer has a German character umlaut (Ü). The actual PDF invoice is good and shows the German character properly,