I had the same problem and it was only fixed temporary by restarts. Since i turned off the advanced wi-fi option "keep wi-fi on during sleep", everything works like a charm. It seems there is a problem with the (deep) sleep states. I am on the newest firmware (rooted, knox 0x0) btw and Android OS went from 60% to 10% battery usage!
So in case the problem returns, try it... You might have a little bit more mobile traffic depending on your apps and configuration, but hopefully this will get sorted out with a new firmware.