I've had this occur to a friend and was able to assist with patience and thoroughness
FIRST:
If a message says that iTunes can't back up your device because an error occurred, check that you have the latest version of iOS. Then open the App Store on your iOS device, tap Updates, and make sure that all of your device's apps are updated. If you need more help, contact Apple Support.
Reconnect. If still not resolved:
- Make sure iTunes is updated to the latest 12.7.1.4 version
- All devices need to be updated to 11.1
- Make sure your computers are updated completely
- Make sure your cables AND ports are knowns goods/they work with other's devices connected to the pc, for example
- Put phones in recovery mode once connected
- Disable security software
(See below for more entailed steps)
If a message says that iTunes can't back up your device because an error occurred, check that you have the latest version of iOS. Then open the App Store on your iOS device, tap Updates, and make sure that all of your device's apps are updated. If you need more help, contact Apple Support.
- Make sure that you have the latest version of iTunes.
- Connect your device to your computer with a USB cable, then select your device in iTunes. If your device doesn't appear in iTunes, you need to fix that issue before you can continue. Or, if you forgot your passcode or your device is disabled, learn what to do.
- Turn off both your computer and your iPhone, iPad, or iPod touch. Then turn them on again.
- If you use a Mac, skip this step. If you use a Windows PC and iTunes won't respond or your backup never finishes, you might need to update, change, disable, or uninstall your security software.
- If you own more than one computer, try to make a backup on your other Mac or PC. Or, use iCloud to back up your device and restore from your iCloud backup.
- If you see an alert that says an error occurred, your backup is corrupt or incompatible, or there's not enough disk space, find your error message below to learn what to do next.
- Contact Apple Support.