Hi Michel,
The Corsica GRIB is produced on a different server (more powerful) running a newer version of WRF and also with different physics scheme settings as allowed be the extra power. All these factor have shown that they give better predictions in general.
The server running production for France 12km, Gulf of Lyon and Nice 4km is using an older version of WRF with settings that occasionally exhibit an over sensitivity to convection events as shown in the cyclogenesis event seen in the Nice GRIB.
The plan is to replace the old server with one, not quite as old, in the coming months and the forecasts will improve.
Best,
David