OK. Thanks.
Usually I click on the extended HD items when I want to remove it, and when given the choice to eject all, I click that and then remove the external drive. I don't have to reboot anything. Never have. It always works.
That is the proper way to disconnect an external drive, but in this case there are other things going on. If nothing else just put it down to my personal sense of computer propriety 😉
Clarification: You're usually booted into your internal SSD, so you can eject your external HDD with no issues.
In this instance, though, you'll be booted into your external, and
you CAN'T eject the drive/volume into which you're booted.
