"Error Could not fetch dependencies" when trying to install private npm packages

🐛 bug report

Preflight Checklist

• I have read the Contributing Guidelines for this project.
• I agree to follow the Code of Conduct that this project
  adheres to.
• I have searched the issue tracker for an issue that matches the one I want
  to file, without success.

Description of the problem

We have a private codesandbox that is linked to a private GitHub repository. In this, there are a few private npm packages.
I have already put in the npm registry token and scope for the account (Registry Host: npm), but it still fails to install (commenting out the packages makes the codesandbox work).

How has this issue affected you? What are you trying to accomplish?

We are unable to get the sandbox to work correctly. Private npm packages will not download successfully.

To Reproduce

• create a private codesandbox that is linked to a private Github repo
• the package.json should have a private npm package that is on the npm registry
• add the relevant npm token that allows the account to download the package
• go to the codesandbox

Link to sandbox: link (optional)

Your Environment

Start with the package.json in a private CodeSandbox linked to GitHub, then reproduce the install using a private npm package and the configured registry token and scope. Done means the private dependency installs successfully without the “Could not fetch dependencies” error; no source file or test is named in the report.