I lost 10lbs over last 2 months or so, my bench only fell from 325 to 315. 20lb drop seems like too much, have you been eating higher protein during the cut? Are you getting your carbs in before the workouts?

20 lbs is a lot. Are you sure all the conditions were the same between each test? How much weight did you lose? In my experience bench is the lift most affected by weight loss.