There are quite a few people complaining about the Xperia Z wifi.
mine works great 98% of the time - the other 2% requires a restart and normally all data doesn't work.
its bloody frustrating that such a simple thing is problematic.
i am trying leaving stamina mode off - today my battery life was 8 hours standby stamina on, 7 hours standby stamina off??
that seems wrong to me as well?