When I update WP Smush Pro to 2.7.7 on a site (not wpmudev.syntric.com) it causes the Add Media button to stop working in the content editor. The javascript console shows an error when loading the edit-post.php page and generates an error each time the Add Media button is pressed.
Deactivating WP Smush Pro restores the functionality.
I tested on a site where WP Smush Pro hadn't been updated yet and reproduced the problem.
I have opened up WPMUDEV support access to http://wpmudev.syntric.com. Feel free to use it to confirm.