I installed OS X 10.10.4 and right at the end of the process, my iPhone (which was plugged in to the Mac via USB with a Personal Hotspot connection) vibrated as if the USB cable had been reconnected, the Hotspot connection disconnected and hasn't worked since.
Connecting the iPhone via USB makes it vibrate and start charging as expected. Connecting to the Personal Hotspot via Wi-Fi works normally. The iPhone has been updated to iOS 8.4.
What's this all about?
I had previously gotten this working, here's how:
Odd. I started up Xcode 7 beta, it asked to install some updates / additional components. My iPhone was connected via USB this whole time, and immediately after the updates were completed, I heard a sound on my iPhone: the Hotspot connection was on again.
But today, the Hotspot stopped working again in OS X 10.11 beta (my iPhone also has iOS 9.0 beta now). Same symptoms, but this time, launching Xcode 7 beta won't help. What to do?