What causes lines in the middle of a 3d print? Solve under extrusion problems mid print, halfway up!

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Why does my top layer look so bad? The rest of the print is perfect : r/3Dprinting

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reprap - Under extrusion towards the end of the print - 3D Printing Stack Exchange

3D Printer Over-Extrusion: 4 Simple Solutions

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Mid print under extrusion? : r/ender3

Under-Extrusion Simplify3D Software

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