iOS 11.4.1 update brought a new feature called USB Restricted Mode. What is this, you might ask? In a word -- security. Apple is trying to improve the security of your iOS device from being broken into by hackers. It's a bit of a convoluted story, so to better understand what this is all about, here are two articles to read:
Apparently some people haven't been able to charge their iOS device if it's been over 60 minutes since it was unlocked. I haven't noticed any charging problem, but in case you have, the articles explain what's going on.
The FBI, for example, would like for Apple to leave a 'backdoor' into iPhones so the FBI could view what a suspect's iPhone had been used for. So far Apple has refused to do this. If there's a 'backdoor' available, a hacker will eventually find it, and all iPhones will be at risk -- not just the one the FBI might want to get into. Arguments can be made for both sides of the issue, I guess. But I'm with Apple on this one.