Cause:

This may occur if:

When printing in full color including the clear toner and the special color is set to high quality/printing in full color including the white toner
If there is an image using cyan, magenta, yellow, or black toner around clear-toner images.
Slippery paper is used

Special color mode is available for Pro C7100X, Pro C7110X, Pro C7100SX, and Pro C7110SX.
To adjust the following settings, pre-register the type of paper in use as a custom paper. For details about registering custom papers, see "Registering a Custom Paper", Paper Settings.