Having the same issue on the latest beta. Seems to happen when the connection switches. either wifi to cellular or cellular to wifi or wifi network switched.I'm currently on 10.1.1 but I think I've had it happen on all the iOS 10 versions. I usually have about 4 tabs open and sometimes when I come back to Safari the latest one is blank like a new tab. I don't know if it's some sort of RAM management glitch or what.