Update Side Effect
Sure thing, every one wants their iPhone updated. However, some unfortunate iPhone users has this dilemma after updating their iOS. Your wi-fi connection suddenly messing on the picture. You'll think you did something wrong upon installing that latest version of your iOS.
Here's the deal. Some phone are not suited for that iOS, thus if affect your wi-fi. If this case will happen to you, here are some ideas on how to deal with it.
1. Reboot iPhone, iPad & Modem and Router
          - This looks quite silly solution but it works sometimes.
2. Forget Wi-Fi Network
     - After successfully "forgetting" a particular network in your wi-fi setting, of course, reconnect it again. Let's see if it work this time.
3. Reset Network Settings
     - If the latter way does not work try resetting the entire network settings on your iPhone. But note that after performing this action you will lose your current cellular and Wi-Fi network settings, Wi-Fi passwords and VPN settings.
4. Toggling Wi-Fi Assist
          - Wi-Fi Assist helps you transfer to your cellular data whenever your iDevice encounters weak or poor Wi-Fi network. You can toggle this feature ON and OFF to come out this problem.
5. Go for OpenDNS or Google DNS
     - Changing the existing DNS server to OpenDNS or Google DNS can be one of the solutions.
6. Turn Off Location Services for Wi-Fi Networking
    - Disabling Location Services for Wi-Fi networking have yielded positive results for some users; you can also follow the suit.
7. Install updated iOS Through iTunes
     - Many users update latest iOS through OTA; Apple experts don't recommend this practice. Rather, use iTunes to update to the latest iOS. This might fix the issue of Wi-Fi and other issues that might weaken the performance of your device.
8. Downgrade your iOS
     -It does not work with the latest, better be contented with the previous one.

Though there isn't any official solution from Apple team, why wont you try to explore a few possible solutions to this new issues.