Error thrown when trying to use "Import Word Document" functionality

Summary

When trying to use the "Import Word Document" functionality on a page, nothing happens.

Steps to Reproduce

1. Go to any page
2. Click on the Ellipsis (...) > Import Word Document
3. Click on Select File to Import

Expected Behavior

A prompt to choose the file to be uploaded should appear

Actual Behavior

As soon as the page below loads, an error is thrown in the console:

https://INSTANCE.atlassian.net/wiki/pages/wordimport/wordimportupload.action?pageId=SOMETHING

The error is the following:

Then, when clicking on the button, nothing happens.