See if a crash dump is created.
I suspect what's happening is the Opus window viewing the destination folder is trying to inspect the files when they are half-written (e.g. to work out what to display for whichever columns you have turned on), and something is crashing because it doesn't properly handle an incomplete file. If you are copying video files then it's most likely not Opus itself but a video codec (which often fail to deal with partial files properly, but can usually be fixed by finding an updated or alternative codec/splitter). Otherwise it might be a viewer plugin, or code within Opus itself. If a crash dump was created for the crash then it will hopefully point to the component that's crashing.
Also, make sure you're using the latest version of Opus (grab the beta version that's linked in my signature to be sure), as there were some bugs in the early versions of v10 to do with parsing some file types, which have since been fixed.