WD External Hard Drive Does Not Appear In The Finder Window

MacBook Pro (Retina, 15-inch, Mid 2014)

OS High Sierra 10.13.1

2.5 GHz Intel Core i7

16 GB 1600 MHz DDR3

Macintosh HD

Graphics: Intel Iris Pro 1536 MB

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Western Digital 8T My Book Thunderbolt Duo

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Yesterday I updated the operating system on my MacBook Pro to High Sierra 10.13.1. Afterwards, my Western Digital 8T "My Book Thunderbold Duo" external hard drive worked like normal for about half a day. Now, when the thunderbolt cable is plugged into the notebook, the hard drive still powers up, but the computer doesn't show the the hard drive icon in the Finder window under Devices. Interestingly, the hard drive does recognize that it's plugged into the notebook because it does power up when the thunderbolt cable is plugged in.

For the purpose of troubleshooting, I unplugged the thunderbolt cable from the notebook and unplugged the external power source for 1 hour before powering up again and plugging in the thunderbolt cable. This resulted in no change. The hard drive still powers up, but the hard drive icon does not appear in the Finder window.

Separately, I installed a different Western Digital hard drive that operates on a USB cable. This hard drive was immediately recognized by the notebook in the Finder window and works with no issues.

The unrecognized hard drive is cared for well. It's kept in an area that prevents it from being jarred, it's kept cool and the dust is minimal. Unsure if the issue is related to the OS upgrade, but this seems to be the only thing that has changed.

If someone can advise me how to fix this issue, I appreciate your assistance.