WE (Windows Explorer) is to Yugo Truck of file copy/transferal. When I want to copy a lot I use RoadKil's Unstoppable Copier. There are other apps like this but I'd share what I use.
I'm on Windows 10 Pro x64 & for as long as I can remember I've had issues transferring files from my Desktop to any connected devices (cable & wireless) although it does happen quicker on a connected Android TV box. It doesn't matter what the files are or how large. I can transfer successfully for a little while & then the process will just stop, Windows explorer will then perform incredibly slowly often displaying a 'working on it' message & sometimes never loading again until I reboot my Desktop, which I always have to do after transferring as the performance is dreadful otherwise. My PC performs great generally & I have no issues with anything else.
Any help would be greatly appreciated.