XPS SimplePipelineFilter producing zero-byte .prn file

I created a printer driver using the SimplePipelineFilter (no changes to filter code). It compiles and installs perfectly fine. I installed it on Windows 10 and set PORT to FILEPORT. That was basically to test it out and see if the output is actually .xps - as per the msdn research that I’ve done.

The issue I’m having is that when I select print, a file save dialog opens with .prn extension, however, when I click save (temp.prn) it just creates a file with Zero-bytes i.e. empty temp.prn file. This should Not be happening, I’ve double/triple checked the code, pipeline configuration and spent 2 days trying to figure this out but can’t find answers anywhere.

Does anyone know whats going on?