I don't usually use a Mac but I need to test this for students who do. I know I had the Create Agent working just a couple weeks ago. Today it doesn't. I've re-installed several times and nothing. When I click on the black Arduino icon in the LaunchPad nothing seems to happen. I am using MacOS High Sierra and Chrome. I also tried downloading the Firefox version from Github and got no better result.
I did briefly see an Arduino icon appear at the top of my screen by the power icon but it quickly vanished.
I have restarted and nothing works.
Did something change recently?