I've experienced that Google Cloud Shell Editor doesn't load, it keeps on loading resources forever. I've tried to restart my instance multiple times. I've changed projects, trying the boost feature, I've even reset my home directory, but nothing works. I've experienced this before and then it has resolved by itself after a few days. But that is not an optimal solution since I'm a frequent user of the editor. Today I experienced it again.
I think I found a solution I want to share with others who experience the same problem. The reason for not loading resources is an authentication problem. If you open dev tools > console in your browser you will see you get multiple 405 errors. I solved this by running gcloud init in the terminal and then reload the editor.