The pillow effect occurs when the amount of infill, temperature and top layer do not match. These 3 things can be adjusted to get rid of this effect.
When the printer is about to begin the final layers, it basically starts making bridges all over the top surface of your model. If you have too little infill, the plastic will have to reach very far before it is held up by the infill. By choosing more infill, there is more material to support the top layer from below and the pillowing should disappear.
By lowering the print temperature you can shorten the time that elapses from the plastic leaving the nozzle until it solidifies. Try lowering the temperature by 10 degrees (but no lower than 190 degrees, or whatever the minimum temperature is for your filament) and see if that solves the problem. This can help with the deformations but can in turn result in during extrusion.
Use several top layers
If you only have 1 or 2 top layers added, it can help to set it up to 3 or 4 to give the plastic more material to even out on top before the print is completed.
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