AoeII: Age of Kings. CPU allies die in beginning?

Hey guys,

I recently found out that I had AoE II: Age of Kings on my old laptop and I couldn't resist to play it again.

I only play the singleplayer mode against the CPU. I'm on a team with two CPU controlled civilizations against three CPU enemies.

However, after the game has progressed for 10 minutes at least one of my teammates and and often an enemy is already "striketrough" in the diplomacy menu.

Apparently that means that they are dead, even though they have a town center and villagers left. Is this a bug? Can I do anything to prevent this?

Any help would be much appreciated.