I think I know why the goblin freezes. Am not sure but I think it's the when he gets shot from the direction he wants to walk towards.

If he is still standing and just about ready to run away again and in that second gets shot, he will freeze.

My mate was following from behind and I went from the front in order to corner a goblin today and shot my first shot at the goblin right at the moment he wanted to run again. And it froze