WD my book issue

[AxeFace]

I bought a western digital my book 4tb like a week ago, yesterday i left my pc on to transfer stuff into it during the night(around 600gb), today i checked and it was still working as usual and i transfered another 300gb, after that it still worked ok. But then later i tried opening a folder where most of my stuff was and it couldn't open popping an error from windows saying that some file transfers were interrupted which wasn't the case or at least it didn't seem like it was the case because i didn't even touch my pc while it was transfering and it also finished without issues. I ran the system error scan and it popped the same thing about files which were interrupted while transfering and it deleted almost all 900gb i transferred with only a couple gbs remaining from the transfers of the day and older stuff still there. A friend of mine told me that it was probably a root index corrupt and that i had to format the disk or a malware.
So i ended up formatting it and starting to transfer the stuff all over again.
What exactly happened? because it never happened to me before and what is a root index corruption? and should i be worried that there's a problem with the disk or use the warranty to change for a new one?
S.M.A.R.T info is all green, error scans and other scans say the disk is good but i don't wanna risk losing my data again like that because i'm moving abroad and taking my data with this external drive.

 

[smorizio]

with usb drives make sure your motherboard chipset driver and usb driver are up to date. also with large file moving make sure power savings is turned off on the usb ports and the pc. if the pc goes to sleep in the middle of a large file move the files may not make it over in one piece.

 

[AxeFace]

I was using a desktop pc with sleep and power saving options all off and all drivers up to date, also the error showed up after i already finished transfering and checked everything was working once, so the claim that something was interrupted during transfer felt strange yet it suddenly could't open the folder even when i managed to trasfer stuff multiple times after with no issues and it deleted stuff from the very first transfer yesterday that didn't trigger anything before and seemed to be working fine. What i mean is everything was fine for like 2 other transfers i did after yet the error appeared and deleted everything from the first transfer which makes me think something became corrupt