I have recently ran into a bug which is quite annoying and have yet to find anybody else who has had the same problem. I am posting a video which displays my problem pretty clearly, but I will explain it here as well. After I surpass a certain number of polygons, my cycles preview render seems to display only part of my mesh based on the angle I am looking at it in my viewport, however I can get around this by using the normal F12 render. It’s an easy workaround, but I really enjoyed cycles capability of tweaking materials live to see the result. I have tried changing back to CPU rendering which does nothing, as well as importing the model into a new project and rendering, still no difference.
If anyone else has had this issue or has any thoughts, please respond, would enjoy being able to use the full capabilities of cycles again.