I would recommend you sign out and log back into your user before trying again. If this does not resolve, here are more steps to resolve:
Refresh the page: Reload the browser to see if it resolves the problem.
Clear browser cache: Delete cached data and try accessing the sandbox shell again.
Use a different browser: Try another web browser to check if the issue is browser specific.
Firewall and proxy settings: Verify network settings to ensure they're not blocking the connection.
Incognito/Private mode: Open the sandbox shell in incognito/private mode to rule out browser-related issues.
You can mark it 'Accept Answer' and 'Upvote' if this helped you
Regards,
Abiola