why photos run in the back

Let’s check another thing, go to Settings > photo > iCloud photo.

and see if there’s anything is downloading Or upload from iCloud.

In addition, try turn off the iCloud photo and then turn it on.

Hello,

Hmm, it shouldn't cause any issues.

However, if you are concerned, you can shut down the Photos app:

1) Swipe up from the bottom of the screen to open the App Switcher

2) Swipe right to locate the Photos app

3) Swipe up on the Photos app to close it.

See this for some charging tips:

When to charge your iPhone or iPad

Good luck.

Do not make a habit of closing all apps. It takes more system resources to restart an app from scratch than it does for a suspended app to pick up where it left off , Apps that you’ve used will remain on standby, but they’re not open and won’t slow your iPhone down. You should only force close it when an app isn’t working properly or is unresponsive

Since it happens at night as You said I think it has something to do with syncing iCloud photos or do you sync your photos on your computer? In addition, make sure to update your phone to the latest version ☞ Update your iPhone, iPad, or iPod touch - Apple Support

In this case I will ask you to contact Apple Support ☞ Contact Apple for support and service - Apple Support

Your welcome ㋡

please keep us informed!

Your welcome ㋡