What would corrupt files on network hard drive

[Hashiriya415]

I have a primary hard drive in my desktop and backup USB hard drive attached to router. I just noticed some videos are corrupted on the USB hard drive but fine in desktop. I'm wondering what would be the cause. I copied the files a couple of months ago to both hard drives from my SD card. For example a 30 minute video had multiple parts where it was corrupted. And it is on more than one file. This particular video was large from gopro 4K camera if that matters. Hard drive is 8TB Seagate Expansion connected with USB to router and to desktop with cat5e. Are there some tests I could run to figure if there is a problem or would could it be? I understand that sometimes these things can happen, but multiple files that are not too old... And multiple parts of the video. Seems like something is not right.