Sometimes specific versions of Word have trouble with add-ins in small ways. The ultimate solution to any problem that can’t easily be diagnosed, is to update the version of Word you’re using to the latest version. Here are detailed instructions for doing so.
If “Update Options” is missing and there's only the “About” button, you either have a volume license install or your company is using a Group Policy to manage Office updates. Try Microsoft Update or contact your company help desk.
If that doesn’t work, please see Microsoft’s official add-in troubleshooting documentation.