I have this older external 2TB Hard drive that has been connected to my older iMac (It runs on Sierra) for a few years. No problems at all. I figured I would move this external to my newer 2017 iMac (runs on Mojave), but this just seems to completely freeze up the computer, it won't even ForceQuit "Finder" I had to shut it off using the power button on the back. When it's not connected, it runs great. I don't have any issues with 2 other externals, both 4GBs, they run perfectly fine on both computers. (I have a lot of Photos, videos, software .DMGs on those...and that's why I swap back and forth) I figured I would just use this 2TB because I barely have any files on this, it's more like a backup of a backup of a backup lol...but no luck. Any ideas? I'm not sure what the issue is. The 4TB drives and this 2TB are formatted exactly the same.