I experienced same problem a few days ago. 0% cpu usage and got stuck at 71%. My problem was some references in my code were wrong because I changed the location of a blueprinted object in context browser. For example, if you have something similar to following code
static ConstructorHelpers::FObjectFinder<UClass> SomeName( TEXT( "Blueprint'/Game/YourProject/SomeFolder/YourBP.YourBP_C'" ) );
make sure that all of the references are correct. Try reversing the last changes you made to see if something recently you did is causing the problem or not. Make sure that all your references are correct.