One likely cause is a dirty or damage encoder strip that is used to track carriage location. This is a thin plastic strip that runs the width of the carriage and has a fine grid printed on it. A sensor in the carriage reads the grid to track location. If dirty it can be cleaned with a lint free cloth dampened with water. Gently wipe the strip until no more stains are found on the cloth. If the strip is broken or missing it would need to be repaired.
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