KM C654 color registration randomly.

[Saghir377]

Hi best wishes for all
Dear i am having one Machine C654 problem in color registration but only appear in cmy and k, mean During printing randomly Appear cmy is printing late and K print earlier on print clearly shows 2mm distance between CMY and K. CMY color registration is good but its not setting with K. But problem is that it Appears some time. when i go and check no problem but customer show me some sample off problems kindly guide.
thanks to all

[Max]

Post examples of test pages cymk full bleed and a test page.