If you have only just updated you may have to accept the situation for a day or two while the phone system catches up with itself. I read that the procedure for indexing, for example, is not fully completed when the download finishes and the background activity is causing the slowing down and excessive battery usage.
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After one week it should be back to normal; however, there are many posters asking about iOS 11 which I have to admit is being reported more often than is usually the case.
I am not from Apple; I am a volunteer helper as is the case with most help here. Except for the hosts, Apple does not read thee columns so any concern about you switching to android will not register. Send such detail to iPhone feedback.
Sorry I can't be of more help.
iOS 11.1.2 has just been released, you may want to upgrade to that version first to see if it fixes things.
Regarding Bluetooth turning itself on: this happens only when you use the Bluetooth button in Control Center. When you switch it off in Settings, it will stay off. Using the Bluetooth button in Control Center will only temporarily disconnect your devices and not really turn it off. It’s off only when the Bluetooth icon in Control Center is crossed out - after you’ve turned it off in Settings.
This is not a bug, but a new design choice in iOS 11 - same is true for WiFi by the way.
Question: since the latest ios update my iphone response time is approx. 20% slower, my touch screen just does not respond sometimes and my bluetooth keeps turning on. Any suggestions please?