Agree with @peterg, and empathize with you @bkm.
I constantly struggle with creating clean PDFs from Print Formats. I have a few Open Issues on my plate right now, where images aren’t being displayed. Or the layout (columns, alignment, spacing) is drastically different.
I think sometimes the main CSS framework used by ERPNext (Bootstrap), isn’t properly loaded when wkhtmltopdf does the conversion into the PDF.
I especially struggle in development environments where I’m using port-based Sites, and no TLS. The routing isn’t always clean, so the wkhtmltopdf cannot fetch all the assets it wants.