I've had KM in the past (Xerox now) and I suspect it is the way the paper path works. Unless they have changed things from 5 years ago, the paper needs to make a rather sharp 90° bend and wrap around. This causes an issue with heavy stocks. The trailing edge with flap.
In your paper catalog on the press for the offending paper, select change settings, then expert settings (near the bottom left of the screen on our C3080) there are 4 controls for 2nd transfer lead edge front or back, 2nd transfer rear edge front or back, adjustments at the top of the page. Depending on whether you are printing face up, or face down, enter an adjustment (+40 usually works for us). If it doesn't respond to them, on the next page, lead or rear edge erase quantity may help of you are not trimming bleeds.... Good luck.