Hi,
i have seen the effect on my S3+. After a reboot hash-rate is ok again.

I wrote a skript which does check the hashrate and reboots via ssh. The skript hits about once or twice a day.

Yesterday i have installed the latest firmware https://www.bitmaintech.com/files/download/antMiner_S320141219.bin and had no reboot since then. Maybe only a strange coincidence.