I did discover the bit rates are different. The working 2310 has a bit rate around 3000 kbps and the out of focus 2310 is at 400 kbps. All the camera settings are identical though...?
Have you tried turning off the 3000kbps camera?
Then reset the slow camera or something? Just to see if it negotiates at a higher rate?
You are using fixed quality?
What and how are you viewing with? The firmware? D-view cam Windows software? d-view cam mobile? mydlink.com website? mydlink lite on app store? or whatever else.. lol