Whilst PLA is not as hygroscopic as other materials, the bumps may be caused by damp PLA. Check out Filament Drying Recommendations | Bambu Lab Wiki to determine if drying the filament may solve this.
Flow Rate Calibration | Bambu Lab Wiki is also worth reading (see the point about “zits”)
Also check the Creality Silk PLA specs on the box/website and confirm that the temperatures for this material have to be changed slightly from Generic PLA settings.