Let me share this workaround I have, @david218.
In the meantime, you can resend back the invoice that has the issue. By doing so, the customer able to see the invoice PDF now. Let me guide you on how.
I've also added an article about "what's new with QuickBooks Self-Employed Invoicing?" This will provide you the details about the recent update that we released to enhance customer's experience when creating an invoice.
Here's an article you can read on for more details: Create an invoice in QuickBooks Self-Employed (QBSE).
Please keep on posting if you need more clarification. Take care.