1. You are not plunging in far enough???Probably not the answer but it could be the case.
2. Your Cutter needs adjusting a little say 1.5mm further out. There should be an adjuster knob somewhere, there is on my DeWalt, though I didnt need to touch it.
Just thought of a possible 3rd, have the biscuits been kept in a dry environment or have they been left out, possible they have swollen a little with environmental humidity.
The moving finger writes....and having writ moves on...nor all thy piety nor wit shall lure it back to rub out half a line.