Sudden GH/s drop in BFL Miner
Both BFL hardware and software are quite unstable, and depend on the starting temperature of the BFL hardware.

What you can do is: stop the mining software, power off the BFL miner, and stick the BFL miner in the freezer for 5-10 minutes (or longer, say 1-2 hours) so that it can cool down. 

When I got my 50GH/s, it could only run at around 25GH/s. Eventually, I found out that it is temperature sensitive. I have, once in a while, powered it down, put it in the freezer, and then powered it back up.

I get pretty impressive results that way. From an original of 8 out of 16 chips working, I now get 15 out of 16 chips working.