Transferring videos from gallery to external storage (hard drive) error

I’ve been trying to back up some videos from my gallery to an external storage (it’s an on the go USB drive with 1TB memory. I just plug it into my phone and I can store extra files in it). I haven’t had any problems transferring photos but when I try it with videos, I encounter some errors. The thing is, it seems to happen randomly. Some videos transfer with no problem while others do not. Then often times, videos that have previously transferred without any problems, suddenly get corrupted or become unplayable. I thought it was an issue with longer videos but it also happens to short ones (ones that are under a minute). I am completely at a loss.

When I first started moving the videos (I select the video and choose ‘save to files’), I received the error “The operation couldn’t be competed. Attribute not found” Or “The Operation can’t be completed. Couldn’t communicate with a helper application”. So I tried to modify the videos a bit (cutting and cropping) and saved them as new videos. This seemed to have worked for others, but not for the rest. Like I said it’s a bit random. I’ve also tried exporting unmodified original but that never worked. Please helpppp