Uncaught DOMException: Failed to execute "send" on "XMLHttpRequest"

If this error is received in static/console or any C3 AI Suite web interface, simply refresh the page and re-establish connection from your browser to the C3 backend.

However, if it is thrown by the UI Provisioner tool (ERR_CONNECTION_RESET on action=exec), refreshing doesn’t seem to work.
Some people have worked around this by provisioning with another web browser, but this doesn’t always work.