Photos import to PC as 1KB files
Every few weeks I connect my iPhone 6 to my PC to backup my photos/videos. On my PC I open 'Apple iPhone\Internal Storage\DCIM\###APPLE' and copy/paste new files to my PC's hard drive. Often the files get copied incorrectly, as shown in the screenshot below. Specifically, many files show up on my PC as '1 KB' in size, when they are much larger on my iPhone. For example, IMG_2521 is 770 KB on my iPhone, and IMG_2527 is 84,824 KB.
This is very frustrating because I keep having to re-copy/paste the files, and what should be a 10-minute task often takes hours. What is going on and how can I fix it?
iPhone 6, iOS 10.1.1