I have 2 different wifi networks in my home, before ios9 I have no issues at all with my home network, after installing iOS 9 all the time disconnects the network and change it to the other one. The most amazing thing is that iOS 9 try to connect to a farther network. I only installed iOS 9 in my ipad air 2, I have not try it on my iphone but Apple changed something in the network that causes this bugs. Even if I am near my router with network A, my ipad air 2 tries to connect to network B that is almost 30 feet away. I have try to reset network settings and nothing, also I disable Wi-Fi Assist and it is the same. If apple don't fixes this issue I will have to go back to iOS 8 to avoid more issues.