I started experiencing the same bug mentioned at Unable to select domain to publish running ChromeOS 50.0 - #10 by coolest_vlad - Bugs - Forum | Webflow. Publishing to a public domain isn’t allowed unless publishing from Site Settings is done first. In my case it seems like it happens once hosting has been enabled.
OS X 10.11.6
Chrome 52.0.2743.116 (64-bit)
Safari 9.1.2 (11601.7.7)