This is a problem I've had for months but only now have got round to finding out the issue. My MacBook Pro seems to have trouble connecting to wi-fi networks. When it wakes from sleep it takes about 30 secs or so to find and connect (the wifi symbol in the toolbar does that up-and-down animation). Even if I leave my Mac on and open, once the screen goes to sleep when I come back to use the Mac, it has disconnected from the wifi and I have to wait another 30 secs whilst it reconnects. This also means emails etc. don't come through. What is the problem? If it's helpful I have a TP-Link Archer VR600 router.