Unfortunately, without seeing your session and document classes and how they are configured, there's little we can do to help you.  Here are some ideas, though:

1. Form Identification might help in the cases where a vendor uses a logo or stylized text instead of OCR-able text
2. If it's naming the file, but failing identification, then you should check your First Page Identification conditions for your document class and also the current Unidentified Documents settings (to see how it is naming these files).  If the file is already named with the vendor before being processed by Quick Fields, you can access that information with a token.
3. You might be able to use other text on the invoice (e.g., the vendor's address) to help identify the vendor.

I'd also recommend contacting your Solution Provider because they often have expertise with configuring Quick Fields and may be able to help you troubleshoot.  And if your Solution Provider can't resolve the issue, they can open a Support Case to get additional help.

If you have access to Laserfiche Cloud, there is a Smart Invoice Profile feature that would likely work even better than what you're doing with Quick Fields (and would be much easier to configure).