You can try these solutions to kick this issue out.
Potential Solutions: Software Update and choose Download and Install if you have the option.
Some users complained that their i Phone run slower and isn’t as nippy as it used to be after i OS 11 update.
If you are still using an i Phone that’s two or more generations old, like i Phone 5/5s/6/65s/6/6 plus/6s plus, then you may be troubled by this issue.
Some users reported that their i Phone’s battery started to drain rapidly after updating to the latest i OS 11, if you’re experiencing this problem and wondering how to fix battery drain on i Phone, you might as well try the following methods.
Potential Solutions: Turning off the Raise to Wake feature has been said to help some users.
Potential Solutions: As with every i OS update, some i OS users have run into the unfortunate situation of not being able to update their i Phone or i Pad using the over-the-air (OTA) Wi-Fi method when updating both their i Phone and i Pad.