Clone Hangs when Using Git Submodules

Symptoms

My project is configured to use git submodules, and the clone step is hanging.

Resolution

If your project is configured to use git submodules and the clone step is hanging, verify that your submodules are configured to use either the relative path or the SSH path to the submodule.

More Information

This stack overflow post has an excellent example of using relative paths.
https://stackoverflow.com/a/44630028