It seems, however, that pressing matters may have forced Apple to nearly silently roll out its USB Restricted Mode feature in the new iOS 11.4.1 update. As it typically takes more than a hour to get a warrant for police to be allowed to use a Grayshift box, this is quite a significant roadblock. Naturally, due to how often people use their iPhones, it is uncommon for the device not to have been unlocked in the last hour. This means law enforcement agencies simply need to connect the phone to an accessory as soon as the suspect is apprehended, and leave it connected as they transport the device to a facility for data extraction.
The restricted mode was put into a beta version of the latest update and has made it through to the final release, making it virtually impossible for law enforcement (or others) to gain access to someone's phone before the USB port is shut down. But for now at least, iPhones, with this update, are locked down.
There should be no reason why iOS 11.4.1 has caused issues on your device. Limitations in the MFI specification may make this easier to say than do however. If you go to Settings and check under Face ID & Passcode, you'll see a new toggle for USB Accessories. These bypass the usual restrictions on entering passcodes by attacking through the Lightning port.
Essentially, after one hour of non-use, an iOS 11.4.1 handheld will not talk to any device plugged into its charging port - other than to receive power to charge its battery - until a valid passcode is entered via the screen. "The ability to postpone USB Restricted Mode by connecting the iPhone to an untrusted USB accessory is probably nothing more than an oversight", Afonin admits.
iOS will prompt you when the update is ready to install.