I'm not sure that, as an *G you are always entitled to +1 luggage, even on normal star-operated flights. Did you book the GoLight fare?
For example, all the light fares on any of the LH-group airlines will definitely not come with free luggage, even if you hold the highest tier of their own FFP.
The flight you mention is a codeshare operated by a non-star airline. Normally alliance benefits don't apply when the flight is operated by a non-alliance member right?