Laser Cutting Better On X-Axis than Y-Axis?

[hube268]

We were cutting some 0.25" Delrin with our LightObject 80W laser. The laser cut the internal holes and X-axis cuts very well but the Y-Axis cuts were not cut through even after several (~8) passes. I checked to ensure there were not multiple lines with different cut settings. Only one line with a single cut setting. What could cause the difference between cuts of X-axis (horizontal lines) vs. Y-axis (vertical lines)? Laser alignment issues would affect both horizontal and vertical cuts right?