@Tony I have parental controls enabled.

It's not so much that it stalls, it's more that the router firmware seems to crash. Once it's gone down, I can't join the Wi-Fi network, nor access the Web UI. Only NAT packet routing keeps working.

Is there a limit on the power you can draw from the USB 3.0 port? I was using a external 2.5" USB 3.0 drive, which should in theory be under the 900mA limit (but I've never checked, to be honest).

I tried again with a 16GB USB flash drive, formatted FAT32, and copied the files from a Windows 10 machine. This time only the Windows Filesharing part died, meaning \\192.168.0.1 just gave an error. The Web UI and FTP function still works though.

@thejpster 

If the external drive has a power supply that would be recommended to use, like you mentioned the port can only provide so much power.

What was the error the computer got?

@Tony Same thing happening with me, just bought an Archer C7 recently. Trying to use the router usb function as a backup drive over the network. The router crashes randomly after a while when copying / synchronizing files/folders. SMB or FTP, doesn't matter, crashes with both methods. Happens with simple copy operations too. Latest firmware didn't help. The connected drive is a 2TB NTFS hard drive in an enclosure with external power supply. Pretty pathetic, that even a simple thing as this, cannot work reliably when it is a TP-Link product. Im angry, considering the main reasons why I bought this router is this very function. Didn't ask for anything fancy at all, just some port redirects and this. Trying to fix this problem wasted a good amount of my time of the day, without solution at the end.