Invoice PDF without name (just .pdf)

Hi all,

Since I updated to v26.6.7-3638 the following problem occurs:
When making a sales-invoice and saving it as a pdf.pdf (or sending directly as e-mail) the pdf doesn’t have a name, just its’ extension .pdf.

It only occurs when I am using my custom theme which before was working fine.

Using Linux Mint, desktop version (v26.6.13.3642)

best regards from The Netherlands