BFGMiner and CGMiner use different drivers, you will not likely get BFGMiner to recognize any device with Zadig drivers installed and would possibly have to even delete Zadig before getting the SiliconLabs CP210x USBtoUart drivers to work, not always but some people have had issues with these two coexisting on the same computer. As far as hash rate falling off, make sure to watch what the temps are reporting as well as making sure something else in the house isn't trying to consume your bandwidth from your router.
Thanks for the driver advice, that helped me get BFGminer running.
With my New R-Box I've now tried cgminer versions 4.3.3, 4.5, 4.7, 4.7.1, and 4.8. I've also tried BFGminer 4.10(I think that's the version). I've tried these at multiple frequencies, with different USB cables, on different computers, and on different pools.
The best results I've gotten are with pre-4.8 cgminer versions running 270 to 290 MHz. These results are typically about 90 GH/s reported by cgminer with lots of errors, pool-side usually comes out to low-70's GH/s with 15-25% error rate. cgminer 4.8 starts out around 70-80 GH/s, then settles around 45 GH/s with 2-3% errors. BFGminer reports mid-70's GH/s pre-error, but an effective mid-40's GH/s with a 35+% error rate.
I could be wrong... but I think I have a faulty box. I emailed the dealer tonight and I'm hoping they offer to exchange.
