Uninstalled Secure Connect Gateway and reinstalled SupportAssist Enterprise (and reconfigured everything from scratch) - problem solved. Will probably ignore any future Dell enterprise software upgrade prompts.
After following a prompt from SupportAssist and upgrading SupportAssist to Secure Connect Gateway, we cannot sign in to Secure Connect Gateway with our Windows and SupportAssist user credentials/details (“We can't continue with this password. Make sure your password doesn't have any invalid characters, then try again.”). Please assist. Thank you.
Cannot sign in to Secure Connect Gateway after upgrading from SupportAssist