You can try relaunching the project. It's important to know that if it's successful, you will lose everything that was in your current R environment (objects created by your script or by commands you entered at the console), and any unsaved changes to open files (whatever was last saved should be OK though).
You get to Relaunch Project from the ... button next to the gear button at the top on the screen that loads endlessly.

If that doesn't work, you'll probably have to wait for a Cloud team member to respond in order to get more help from behind the scenes.