Just installed iOS 11 and noticed “Turning off Wi-Fi from Control Center does not turn off WiFi from the settings in iOS 11”? Yes we all did and thought for a while that this was a bug but it isn't.
Apple today published a support document in which it mentioned that turning off Wi-Fi and Bluetooth from the Control Center temporally disables the WiFi and Bluetooth connection to keep radios on for other features like Apple Pencil, Apple Watch, Location Service, Handoff, Instant Hotspot, Airdrop and Airplay.
In iOS 11 and later, when you toggle the Wi-Fi or Bluetooth buttons in Control Center, your device will immediately disconnect from Wi-Fi and Bluetooth accessories. Both Wi-Fi and Bluetooth will continue to be available, so you can use these important features:
- Apple Pencil
- Apple Watch
- Continuity features, like Handoff and Instant Hotspot
- Instant Hotspot
- Location Services
So take this thing in mind that it is not a bug but Apple intentionally integrated this feature into iOS 11.