Swipe Card Reader: 

Magnetic stripe swipe card readers have been found to be susceptible to Radio Frequency interference generated by the scanner of the MFP (Multi-Function Printer). i.e. when the scan head passes near the card reader, the card reader will reset itself. This will cause the reader to emit an empty card swipe as part of its initialization sequence.

This happens because the card reader with platen cover (open or closed) is placed above the scanner.

To avoid this ensure that while mounting the swipe card reader it is placed in a location where the scan head will not pass near the reader.