Is cycles buggy?

Hi,

My PC is not that good but not that bad either,

fx8300
radeon 7770
16gbram
win10 64bit

I made a 100x100m terrain and sculpted it. In the middle of sculpting, half of terrain just disappead. It happened when camera zoomed out. I thought it might be the camera, but with internal rendere it never happened.

and I was making a kitchen, then suddenly all objects just disappeared. It just happened after I tested some rendering…

and I was making a highly subdivided something----part of the object just disappeard.

It all happened this week, and it never happened with internal renderer or other apps.

and it is sooooooooooooooooo noisy when there is hard lighting. I raised sample to 8000 but there was still noise.
You might say to tweak something to get better speed or results, but that noise is already frustrating.

What’s wrong with cycles? Do I have to use lux renderer? but I can’t use preview with lux renderer.

Check 3d view clip start and end distances
Check camera clip start and end distances
Try orthographic versus perspective views

Unless you’re using the rendered view when sculpting (I assume not), then whether you are in cycles or blender render makes no difference when you’re sculpting