If almost everything cuts except a small area, it could be that the board is slightly warped. If there is even a slight warpage, the laser is out of focus in that spot and might not cut. If you haven’t already cut them, you should cut some honeycomb hold down pins to secure your material securely and flatly to the honeycomb tray. Honeycomb bed holdown pins
Slowing the speed slightly (like maybe 10 less) would probably also help in the short run.