External USB Hard Drive Not Mounting in Sierra

[Huntn]

Frequently when I call it a night, I unmount my external USB drive, turn it off and put my MBP to sleep. Frequently I find that my USB hard drive when turned back on does not mount and sometimes I can see it in Disk Utility and sometimes not. When I can see it if I select the drive and hit the "mount" button, nothing happens. Of note this drive has 2 partitions.

Is this a known issue?
What is the solution? Thanks!

 

[Taz Mangus]

Is this on the 2017 MBP? It could be the drive enclosure. I suggest that you try different USB C ports and see if they all act the same. As a sanity check, try out a different drive enclosure on the computer and see if it acts the same. When all else fails, a call to AppleCare might be in order.

 

[Huntn]

Is this on the 2017 MBP? It could be the drive enclosure. I suggest that you try different USB C ports and see if they all act the same. As a sanity check, try out a different drive enclosure on the computer and see if it acts the same. When all else fails, a call to AppleCare might be in order.

Oct 2016 MBP. Thanks.

 

[lexvo]

Is there a reason you unmount the drive? I always let my iMac go to sleep with the drives mounted.