https://wccftech.com/ios-12-disables-the-lightning-port-if-device-is-locked-for-one-hour-making-devices-like-graykey-box-useless/

As a security measure, you can choose iOS 12 to disable the Lightning port on your iPhone if the device is locked for more than an hour. The feature works on the iPad too.

The GrayKey Box has been making rounds lately, developed by an ex-Apple engineer, allowing access to a locked iPhone using the Lightning port. But it seems as though iOS 12 is going to put all the hoopla to rest with a brand new feature that disables the Lightning port on an iPhone completely if the device is locked for more than one hour. This new feature is also part of the iPad as well.