I read this on Saturday morning 9th Nov, and realised I had not updated my Pi 4 for about a week. So I ran the update / full upgrade.
My update script does a reboot at the end once everything has been installed. Some time recently it suddenly began rebooting ok with external drives plugged into USB 3. That was surprising, and rather pleasant.
After today's update it is back to not rebooting unless I unplug any external USN drives plugged into USB 3 and cycle power.
So I am back to selecting reboot, or typing sudo reboot, waiting until I get a blue 'no signal' screen on my monitor, checking there are NO active LEDs on the Pi, turning the power supply OFF, waiting a couple of seconds, then turning power back ON.
So instead of rebooting it looks like I go back again to shutdown > cycle power, to reboot the Pi 4 for now. Which is not a problem anyway. Except that my update/upgrade script will fail on reboot. A small annoyance - not a problem.
But it was nice to have enjoyed reboot working for a week or so
And no, I haven't changed the drives or what they are plugged into, and NO, this is NOT a complaint. Simply an observation. For me, reboot wasn't working, then it was, now it isn't.
Prior to it suddenly working, there had been one or more firmware updates. And today I noticed there were firmware updates. I wonder if there was any change in USB stuff in firmware, or if it is just one of those coincidences we get to experience with all computers from time to time..
Whatever it is, I'm sure someone in the organisation will discover it and sort it..
In my case, one attached USB 3 drive is self powered via a USB splitter. The other is an SSD via an adapter into the other USB 3 port.