We recently upgraded our site to the latest version of Sharepoint Online. One (and only one) of the document libraries on this site does not contain the expected "Upload files using Windows Explorer instead" option when attempting to upload new documents. This option appears in on every other document repository we have on the same site.
Does anyone know why the Windows Explorer option would not be available in such a limited fashion? I've confirmed all standard setup options to establish Windows Explorer as an option. And everything appears correct. And it appears for every other library within the same site.