PDF conversion failed

Hi,
Everything has been running great without issues until this morning when I went to send out our monthly invoices, I now get “PDF conversion failed” in the send email window and no email is sent.
The PDF button works so it doesn’t appear to be the PDF generator itself.
Nothing has changed on my side and I’ve been using the same version since I started using Manager.io and its all just worked until now.
I have also tested/confirmed that the send mail works

Any help to resolve this will be appreciated as I need to get these invoices out

Desktop Version 25.9.13
Windows 10 Pro

EDIT: On a side note, I have also just noticed that the Theme Editor isn’t working anymore. I don’t know if these issues are related, but I can’t see how. Are these “online” services, even though I’m using the Desktop version?