PC with an internal disc drive writing to an 8tb external.
Most of the errors I get are writing to the external it seems. Usually if I try to do other tasks while handbrake's running and doing it's thing.
Your USB connection is either too slow, or the drive cannot handle that write speed. I used to get that sometimes when I am editing gaming videos in Vegas when I had my old laptop. My new PC has a USB 3.0 port so I use that plug jack for the drive, don't seem to have anymore issues. Not sure what Macs have for that kind of thing.