Currently running Civi 5.49.1 but I've been seeing this behaviour for a little while now. I've got Civi set up to apply VAT (sales tax) and issue invoices, which go out with event registration confirmation emails. All good.
What used to happen as far as I can recall is that if the event was free, then no invoice was created or sent. Ideal.
However what I'm seeing is that participants are being sent confirmation emails with an attached file called 'invoice.pdf' which is blank. Not good.
Before I log this as an issue in Gitlab, is there a recent change in the settings/config around invoicing that I'm missing, or is this a bug that others are seeing?