Some serious thread necromancy, but since it's been hijacked for this new issue... Seeing the same thing on two systems running MacOS 10.12.6 and Safari 11, with the latest Evernote Web Clipper. Reinstalling does not help, logging in again does not help, and "Privacy > Cookies and Web Data" is set to "Allow from websites I visit". However, I do know that Apple significantly tightened what "visit" means, so if you're relying on that functionality to make the extension work, then you're probably out of luck. I'm certainly not going to allow everyone to track me so you can make your toolbar button work.