Document Merge API - CORRUPT_DOCUMENT Error ONLY when I have edited the file.

I am hoping to use the PDF Services API to generate PDF files from .docx template files. When I use the downloadable templates (AgreementLMTemplate.docx, AgreementLMTemplate.json) directly from the Adobe website everything runs smoothly. The API call happens and the resulting PDF is correctly filled out.

The problem is if I make any edits to the template, or create a new .docx file using the Word Plug-in, I get and error with the statusCode:400 and errorCode: CORRUPT_DOCUMENT. It does not matter if I edited the downloaded template or created a template from scratch, any .docx that I hit 'Save' on within word causes the CORRUPT_DOCUMENT error to occur.

Even a .docx with not tags and just a line of text or a single tag create this error. This also happens when I try to use the online tool and create the PDFs from within the Word Plug-In, so it must be something in my version of Word that is causing the error. Word is up to date running Version 2401 (Build 17231.20236 Click-To-Run).

I have uploaded the simplest test file I have tried to create, and even a simple, single-tag doc gives the CORRUPT_DOCUMENT error.