Being a Toro guy I’ve run into this problem many times and there are many reasons which will cause this issue. Check to see if any apply to your cutting method.
1. Underside of the deck is not clean. The SuperRecycler units must be kept clean to work best.
2. Cutting when the grass is wet.
3. Cutting at a too low of cutting height. Never try to cut more than 1/3 of the grass height.
4. Using a dull blade, wrong blade cutting angle or the wrong blade. Toro Atomic blades, sharpened to a 30 degree angle work best. Some aftermarket blades don’t work at all.
5. Engine speed is too low. I set Toro engine speed at 3200 RPMs.
6. Any combination of the above.