I remember on one firmware image I needed to delete the package: gl-sdk4-ddns because it was conflicting and then reinstall ddns and cloudflare. Maybe the reason for uninstalling the package was due to the code you highlighted. By removing the package it also removed some links inside the client GUI however my ddns worked then. The newer firmware I've flashed was good from the off so I didn't need to do anything.
Here was the original post for context: