It seems to disappear once you select a 0.2 nozzle. It is still listed with a 0.4 or 0.6 nozzle. Same for different sized nozzles for my X1C. You can select Generic Silk PLA with 0.4 or 0.6 nozzle, but as soon as you change to a 0.2 nozzle the filament changes to Bambu Silk PLA and the Generic Silk PLA preset disappears.