I have the same setup as Patrick. If I reboot, I always turn off the HDD, and boot that way. After it is up, I turn on the HDD and it mounts no problem.
I have noticed that occasionally (more like every 2nd or 3rd time) if I boot that way, it doesnt boot “unslung” and says that it is running from flash memory. If I reboot, it seems to clear that.
I try not to re boot that often.
Dave