After updating the WordPress Duo security plugin to the latest version, it stopped working on my multisite installations.
I had the plugin network activated which worked fine with an older version of the plugin.
When network activated the plugin doesn't show up in the plugin sections of the network sites. It did with the older version
When I network deactivate it, it does show up, but when I chose settings, I get "You do not have sufficient permissions to access this page." Mind you I am both the network administrator and the administrator of all the network sites.
I checked this on two network installations, they both worked with an older version of the plugin. Now Duo authentication just stopped working. It's now just the plain WP login procedure.