jQuery is not defined for Menus admin page

Hello, and thank you in advance for any feedback or direction you can provide regarding this issue. After days of troubleshooting, I have finally identified a pattern to the unexpected behavior we are experiencing on one of our Multisite networks.

Since the automatic WP update to v. 3.8.1 I have been unable to manage menus on various sites across the network by using the drag and drop functionality of the Menus admin page. Attempting to expand a menu item results only in the page reloading with the item expanded. Dragging an item only selects text on the page. And, the Links tabs, screen options, etc. do nothing when clicked.

Drag and drop on the Widgets admin page on these same sites works fine. The Firefox console reports the following js error upon load of the page at /wp-admin/nav-menus.php

ReferenceError: jQuery is not defined

The Pattern? This only occurs on sub-sites of the network! After checking a half dozen sites on the network, I’m inclined to believe this is the case for all sub-sites. I can use the menus admin page on the main site (ID 1) with no trouble.

So, to recap:
subsite.domain.tld//wp-admin/nav-menus.php = jQuery error
domain.tld//wp-admin/nav-menus.php = no error

Has anyone else noticed this?

For the record, I have made painstaking efforts to rule out any plugin or theme conflicts. I deactivated all plugins on each site, I network-deactivated any plugins activated across the network, and I ensured there were no mu-plugins or drop-ins running.

I encounter the same issue with various themes including Twenty Thirteen and Twenty Fourteen.

I have “reset” the plugins folder.

And I have uploaded new copies of the wp-admin and wp-includes folders from a fresh v.3.8.1 WP download.

PLEASE: What other steps can I take to identify the cause of this issue and resolve it?

I did search these forums, but could not find any similar report. Is anyone aware of this possibly being a known issue?

Thanks again for your time!