It looks like https://github.com/TeamHG-Memex/arachnado/commit/66ef047f3175b7063b7feca4df697b5a18ea8a50 broke it because JS code (e.g. https://github.com/TeamHG-Memex/arachnado/blob/master/arachnado/static/js/utils/Rpc.js) was not updated as a part of this change.