It turns out , that youtube is having a wave of hackers stealing accounts and Astartes is one of them. So forget this link and do not click it. There are a few channels that uploaded a supercut with all 4 parts in one video, so if you really want to see it, maybe search for Astartes supercut, although that will not be the original creators channel either but at least you can watch it without adverts and enjoy this great piece of GCI art.