I’m not at this mission yet. But I’ve seen on Steam Community also people complaining about this particular mission. Same loading problem. Some say it finally loaded in after 10 minutes of waiting. Others say they waited something like 4 hours but it never loads in. I guess it depends on your ram in this case, or something, whether your computer (the program, as in AoE) has enough resources to hold out until the mission finally loads. Just a guess.