My mid-2015 iMac (loaded at the time) has this hiccup where it crashes during file copying. I'm a photographer/cinematographer and my file library is fairly large (a Petabyte), kept on four and five disk RAID Arrays. This iMac has had everything replaced by Apple trying to determine why it does this and nothing has helped. Doesn't matter if the arrays are Thunderbolt or USB, even NAS. Sometimes it will copy files for a day, sometimes for 15 minutes, but at some point it is going to crash, give me the multi language box message and reboot. Obviously this makes backing up files incredibly tedious and hit and miss at best. I'd consider moving to an iMac Pro if I thought it would be any better but given the fact Apple has no idea what's causing it, I am not real confident.