Glass does present a challenge in P11 and Superfly, everything depends on what type of glass material you are using.  And yes, there are different types of glass and how they transmit, reflect, and refract light.  Usually, it would help if you increased your pixel and transmission values to overcome the grainy effect from the render, but this will be at the cost of longer render times. You will need to screencap your glass material shader and render settings to determine where to make changes.