If you are wearing glasses, using a plastic helmet shield and looking throught the Clearview, the combination could be causing just enough distortion to cause you problems.
If you are using a faceshield, try raising it and then lowering it while looking through the Clearview to see if you can detect any difference in your vision. Try the same thing with eye or sunglasses to see if this may cause some distortion.
I agree with NormanB that it's likely you are looking at the Clearview while riding and not through it and this could be causing you some problems. Try not to stare at a fixed point (object) while looking through the shield but keep your eyes moving (glancing) at different points in front and to the sides of the shield.
Hope this helps. I installed a Clearview XXL a while ago. I look through it but haven't experienced any problems. It was somewhat distracting at first until I realized, like NormanB said, I was tending to look at it rather than through it.
Don