Hi Ouroumov. I think it is an issue with the USB.
I installed and tested this with two other files different file managers - Thunar and PCManFM - and they both had the same problem. When copied one at a time, the files copied over, albeit a bit slowly. But, when copied as a batch, they got stuck. But did, eventually copy over. But it took many minutes.
When doing it via the terminal, it was a bit quicker, but not much
But, when copying the files, either via terminal or via any of the GUI file managers, from one folder on my internal hard drive to another, no problems were encountered.