How to fix an iPhone 7 Plus that responds very slowly after updating to iOS 11.3.1

Following the adoption of a new firmware upgrade, background apps may become rogue. Some functions, if not the entire system's operation, would be affected if this happened. Quit all background apps on your iPhone 7 to rule this out. Here's how to do it:

1. Quickly press the Home button twice. A list of recently used apps will appear on the screen as a result of this action.
2. To exit each app preview individually, swipe upon it.
3. When you're finished deleting all background apps, restart your iPhone to refresh the internal memory and operating system.
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