DOCX Cannot be converted to PDF

NOTE: I had made a prior post here: 
Re: Document Generator API Timeout - Adobe Support Community - 14099256
addressing this issue but there have been some developments so rather than reply to the same thread with each development I thought I would create a new post. 

The Problem 

The issue I am facing is related to both 'Document Generation' and 'Create PDF' services.

Essentially, I am trying to use Document Generator with a large .docx file and some JSON to create dynamic content in PDF format (its intended function)

The issue I am encountering, is a status of 504, shown here when attempted through the Postman Collection:

I have had success using Document Generator on smaller files so it doesnt appear this issue is universal but the templates I am dealing with will all be fairly large in size so I need to ensure the Document Generator can handle these types of documents. 

What have I tried 

I attempted to bypass the issue by allowing Document Generator to output another .docx file and then simply convert it to PDF using Create PDF. I did this by specifying outputFormat in the JSON like so:

Document Generator was able to output a docx file that reflected my specifications, however when I went to take this output and run it through Create PDF I was met with the same 504 error. 

Additonal Info

The template I am having issues with had previously been run through a similar tool to Document Generation called Seismic. I thought maybe the leftover Seismic tags were causing an issue but even after completly removing them from the template the issue persists.

Conclusion

There appears to be a problem converting large .docx files to PDF using either Document Generation or Create PDF services. Please advise and thank you.