Install iOS 11.4 If You've Got Performance Issues
iOS 11.4 could also have a positive impact on your iPhone or iPad's overall performance.
While they go unlisted in the change log, iOS updates have been known to iron out issues like severe battery drain, broken Wi-Fi connectivity, and busted Bluetooth.
The iOS 11.4 update could also fix UI lag issues, random reboots, lockups and freezes, and various issues with first-party applications.
We dealt with random reboot issues on iOS 10 and we haven't seen widespread random reboots on the iPhone X, iPhone 8, iPhone 7, iPhone 7 Plus, iPhone 6s, iPhone 6, iPhone 5s, or iPhone SE while running iOS 11.4.
If your device's performance is struggling consider downloading iOS 11.4. Just make sure you read reviews from other iOS 11.4 users before you do.