Internet Sharing stopped working just recently.
Configuration is Wi-Fi shared over iPhone USB cable.
Mac OS version 10.13.2, iOS version 12.4.1.
I haven't updated operating systems of my computer or phone for at least a few months, so it wasn't broken by a software update.
I restarted both my computer and phone numerous times and reset the Internet Sharing from the menu. Nothing works.
The cable is not broken. I can charge the phone over the USB cable, and it gets properly recognized. iTunes opens automatically when the phone is plugged in.
The Wi-Fi connection is not broken. I tested with a browser on the Mac computer and it works normally.
Update: I also reset the iPhone's network settings to factory default and that didn't fix it.
Update #2: Internet sharing works as advertised from Wi-Fi to Bluetooth PAN, so it's the USB internet sharing service/drivers that are broken.
What broke it and how do I diagnose the problem? I'm looking for an error log or diagnostic tool that would pinpoint the faulty link. Probably on Mac OS since iOS is terrible at supporting advanced user maneuvers and diagnostics.