Perhaps the DF is not resting squarely on top of the MFP, and the exit ramp on the glass does not align with the exit ramp on the DF?

If it were me, I'd raise the DF just 25mm or so and shine my flashlight down the slit glass to see if they align, or more likely cross over each other. A good reference is just to stand back a little and observe weather the DF is about square on the top of the machine. =^..^=