When starting the web editor, my board gets found and it states that it is connected. In the drop down menu, only the port is displayed. My connected board which I connected with the sketch is not displayed. Starting "Upload and save" does not work and hangs the "build". Busy button does not react. Selecting the board first makes it work. So either you should force a board selection or save the previously selected and connected board with the sketch.
OS: OSX 10.11.5 Browser: Safari 9.1.1 Driver: ArduinoCreateAgent 1.1