External hard drive causes my iMac Pro to randomly restart... why?

Hi everyone,

For the past several months I have been having an ongoing issue with my iMac Pro (3 GHz 10-Core Intel Xeon W, 64 GB 2666 MHz DDR4) where it has been randomly restarting. Always when it starts back up, a message pops up stating that "your computer was restarted because of a problem".

After lots of troubleshooting I finally zeroed it down to the culprit... one of the external hard drives (a 1 TB LaCie USB 3 external drive). Just like my other drives, I have this drive plugged into a USB hub. When I leave this drive disconnected from my iMac, the random restarts disappear. I have tested and retested this drive (using Disk Utility, etc.) but there seems to be no issues with it, so I don't understand why it is causing my iMac Pro to restart. Can anyone give me some ideas? Should I just go ahead and replace the drive? Normally when this has happened before a faulty drive that was on the way out had been the issue, but there seems to be no issue with this one, so I am just curious to see if there is any other explanation.

Thank you in advance for your assistance :)