There have been several reports of the new iPhones not charging automatically when plugged in. Specifically, initial reports mostly involve the iPhone Xs and Xs Max. That said, further reports indicate similar problems with iPads and older iPhones, meaning this may be an iOS 12 issue.
The reports describe some of the aforementioned iPhone models not charging when plugged in, until they are woken from sleep. Other more egregious cases involve having to wake the phone from sleep, then unplugging and plugging the Lightning cable back in for the charging process to start. Incidentally, there were no reports of such issues when wireless charging was involved.
If you need a visual description of this issue, then the video by UnboxTherapy does a pretty good job at showing it.
According to 9to5Mac, there are people pointing out the USB Restricted Mode as being the cause of the issue. The site continues to explain that the security feature shouldn’t be kicking in when the devices are plugged in through charging bricks.
Makes sense, and if it were simply an iOS 12 issue, it’s also surprising that it’s affecting some devices and not others. Unless, of course, the unaffected devices already had the feature disabled prior to the discovery of this issue.