Corona Light Noise

Hi, I have 2 problems with corona.
First, i rendering DOF scence and the lighting is very noise. I render it with size: 4000x3000 and lost about 30 hours. You can see in my images.
Second, I don’t know why corona don’t use 100% cpu. My pc is dual E5-2970v1. 32GB ram and Corona uses 17GB ram only - 1-2% cpu performance. After i’m reset setting to default and choose “resume from file it’s will be render with 100% cpu”.
How to fix 2 problems? Thank you so much!

Hi, this definitely sounds and looks wrong. Can you report it here? https://coronarenderer.freshdesk.com/support/tickets/new
It would be great if you could also add what CPU you are using, and what version of Corona this is. A sample scene where this is happening would be appreciated too.