Oh, I meant clear the drive (quick format). Then we can see if the first part of the drive is good with any file (expected) but once we get farther along in the spindle, it starts having problems.
Is the external a new drive, a repurposed drive, or something else? I tried 10 and didn't like it so I went back to 7, so I can't give a step-by-step.
What I'm suggesting is:
wipe (delete everything on) that external drive (back up anything on it that you don't have elsewhere!)
Copy a few of the files you are having problems with
See if those work while they are the only things on the drive
IF THEY DO
-- Most likely some of the flash chips aren't working quite right. This may happen on older or poor quality stuff, but rarely on expensive stuff. You'll have to find the way to check flash drives in Windows 10, it was "right click on the drive in Windows Explorer -> Properties -> Tools (tab) -> Check Now.. (button) " in Windows 7, it's something similar in 10 I hope. Then say something to the effect of "Scan for and attempt recovery of bad sectors". It isn't exactly traditional sectors on flash, but close enough.
IF THEY DON'T
-- Most likely something on the files themselves aren't compatible with whatever you are trying to play them on. This could be codecs issue, but it could be others too.
I hope this gives you a starting point!