So, to avoid being that guy, I have figured out what my problem was.
I use Sophos Home as my antivirus, and had added rule exceptions to the woff directory and also to the WOFF.exe & cfs3.exe However, neither of these to things appeared to do anything, nor did Sophos even report that it had blocked anything
What did work however, was adding local exclusions, by opening the taskbar UI -> Help -> Troubleshooting -> Local Exclusions -> Add
My guess is that there is some way in which the Anti Virus runs active scanning which interferes with WOFF, even if it's set to not block anything