I still get this issue in 1.4.10
Also can’t generate PDF in 1.4.10, blank white page.
I had this issue and managed to fix it. It seemed that mpdf was not properly installed during setup. What I did was, in a terminal, cd into the invoiceplane directory and run composer require mpdf/mpdf. After that, everything seemed to work fine.
This is indeed a quick fix for make it working but does not allow you to use the Zugferd XML extension.