I have issues with network connectivity on my O2 iPhone 7S - huge issues - not connecting / connecting hanging / slow - O2 v25.0 IOS 10.0.2. Sometimes switch to airplane mode and back fixes it - other times it does not. (Bought from Apple direct)
I think all these issues are part of the same bug. People on EE, O2, At&T and others have all been complaining about similar issues, it just seems to be worse on some networks than others.
Sometimes when my 7 plus drops back down to 3g the connections is incredibly slow i.e. 2g speeds, and then turning airplane on and off or restarting the phone fixes it. Hopefully a patch will come out soon.