Helmet is a security feature that may cause an issue with the Cluster Manager's Web UI. You may only see this loading screen when trying to access the Cluster Manager with your browser:
Then, you should deactivate the helmet feature by adding this line to the Cluster Manager configuration file
So far, we have seen this issue only on Windows machines running Gurobi 9.1.
If you have experience with the developer console in your browser, have a look there when you experience this issue: On the console you may see an error like "Refused to execute script from '...js' because its MIME type ('text/plain') is not executable, and strict MIME type checking is enabled."