Have a MyBook 4Tb from late 2015. Occasionally the drive will no longer be accessible in windows, it simply disappears from explorer. The only way I’ve found to access it again is to cycle the power on the drive.
Happening with two drives now. Disappear from windows explorer, only way to get them to show up is to unplug their power supply and then power them back on. Rebooting/shutting down PC doesn’t seem to have any affect.