I have a dual band router setup, and I can connect to either band fine at first.
Then, after working fine for a few minutes, the connection *stops*, no errors or warnings, just, nothing. Turning the screen off seems to expedite this, but I could just be imagining that part.
After it stops, turning the screen off, then on again, I get an X over the Wifi icon, but it still shows as connected.
Sometimes, if I switch bands, it will work again, but almost always, I have to reboot to get it to connect again.