Some DVDs stop playing halfway

I copy a lot of movies, but I have a mystery. I'll watch an original DVD in my DVD player and if it plays fine and I like it, I copy it. About 20% of these copies stop playing halfway through and return you to the main menu. You cannot watch the second half of the movie even if you select a scene in the second half. It just returns you to the main menu. I was using DVD Cloner and tried my old DVD Shrink/Encrypter but they stop halfway too. I tried switching media (from Staples to TDK) but that made no difference. These DVD copies play fine in my computer, so I finally I bought a new DVD player and the problem copies still stopped halfway through. What is going on? Is it the problem the DVD player hardware, DVD player software, DVD media, or DVD copy software?

 

Either Netflix or the local library. Both seem to have the same 20% fail rate.

 

I will need to re-obtain the original DVD. That will take a couple of weeks.