Yesterday I ran into the same issue! Copying a .sle file of 45 Gb to an E-Sata drive made the system hang.
I think that I know the culprit. When Windows starts copying the Action Center told me that Windows Defender was (suddenly) disabled. So, during the copying process, I restarted Windows Defender and since that moment copy-speed decreased to an amount of 3 Mb/sec. I tryed to cancel the copy-process, but that killed Windows Explorer.
After a reboot I tryed to copy the file again, but then I had Windows Defender disabled manualy. That did the trick. The copy-process went at the normal speed without any hang or interruption whatever.
I never had issues with smaller files and when copying a folder with a large number of files there wasn´t any problem, even when Windows Defender was enabled. This was the first time I copied such a large file.
It seems that Windows Defender has problems with large files, when you want to copy these.
So, from now on, I disable the realtime protection of Windows Defender when I want to copy such a large file.
Hope that I could help (in my case this was the solution).