Which version of the library are you using? The MQTT format changed for production (v2), so using some staging (v1) version might not expose the meta data?
To see what version is installed:
cd $HOME/.node-red
npm list node-red-contrib-ttn
Today, the current version is 2.0.1.
Meanwhile, in 2019, the support and maintenance for this SDK has been discontinued, it is not recommended to use the SDK for new projects.
(Also, see https://ttnmapper.org.)