While a lot of bugs have been addressed in Android 5.1, most of the devices running Android aren’t able to upgrade yet to the latest version (full list of devices here). However, One issue that hasn’t been addressed is the Wifi problems.
Both Android 5.1 and Android 5.0 experience similar Wifi issues that cause users to be unable to connect to certain Wi-Fi networks or are unable to browse the Internet even after connecting to a Wi-Fi network with a working Internet connection. Bellow are several methods that explain how to fix Android 5.0 Wifi problems and Android 5.1 Wifi problems
While it might sound silly, for most users our first solution to their Android 5.1 wifi problem has worked. We recommend you restart your router first (unplug it, wait for 10 seconds and plug the power cord back in) and then restart your Android device (hold down the power button)
It might be that you are using the wrong Wifi bands (frequency). By default this is on automatic but you might need to manually specify if you are connecting to a 5GHz or 2.4GHz Wifi router. This can be changed by heading over to Settings > Wi-Fi > Advanced > Wi-Fi frequency band. Choose either “5GHz” or “2.4GHz”
Head over to Settings > Wifi and look for the Wifi network you want to connect to. Once found, tap the name and click the “Forget” button. Proceed to switch off Wifi and Back on after waiting for 5 seconds so your device will scan all nearby connections again.
Look for your Wifi network and click on the name to connect again.
If any of the solutions to the Android 5.1 Wifi Problem or Android 5.0 Wifi Problem mentioned above haven’t worked, there is only one option left: Factory reset your device. Keep in mind that this will wipe all of your data from your device. Navigate to Settings > Backup & Reset and click on “Factory Reset” then press “Reset Phone”