This isn't really an answer, it's more like a workaround, but here's how I eventually got it to work:
Instead of using the "FSBackend{FSBackendOptions{}}" nodes, I simply went with the standard "backend" node in the .init method. That seems to have solved the problem.
i18next
.use(FSBackend)
.init({
lng='en'
backend:{loadPath: "C:\Users\myuserpath\OneDrive - MyStuff\QA-Automation\locales\en\NAMESPACEFILE.page.json",},
}
This may be a bug or issue with the FSBackend or the FSBackendOptions. I will have to research it a little more and see if others are experiencing the issue, and perhaps file a bug report.