We are also seeing some issues with one of the CT miners:
The unhealthy miner:
http://imagizer.imageshack.us/v2/640x480q90/849/s1pm.pngAnd for comparison a healthy one:
http://imagizer.imageshack.us/v2/640x480q90/823/5opj.pngMiners are on different networks, and first miner's has been mining a little on the backup pool, so we are suspecting some network issues at the moment.
Local network ping to the miner was healthy all time, so now we are checking external network connection.
The miner has also completely stopped once and had to be rebooted. Unfortunately miner does not expose any logs, but only current stats

Thanks for sharing the issue with not hashing core, we will also try to look for that as well.