Chris,
Probably obvious, but I take it you have Mode-S/3D enabled (and saved) in the Rosetta Config?
Less obvious - do you have Mode-C/S enabled? I could be wrong, but IIRC the Ground Station will only uplink MLAT positions if they are requested by the ‘Airborne’ PilotAware (i.e. your Rosetta), which requires the Rosetta to be directly receiving the Mode-S signal before it will request the MLAT Uplink from the Ground Station.
Edited to remove the third option - I obviously didn’t take in the first time I read it that the airfield info and METARS are uplinking. (I had suggested that the Rosetta might not have been transmitting - i.e. set to Rx Only or no GPS Fix - and therefore wouldn’t trigger the MLAT Uplinks. Sorry!
Regards
Peter