EDIT: Issue only exists on Xbox One X system. Xbox Series X can run up to 8 teams in a skirmish while Xbox One limits you to 4
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Be Subtle achievement asks the player to reveal the location of 300 villagers with one use of the Imperial Spy ability from the Chinese civilization.
The problem is this is not possible on Xbox One without using friends to cheese/boost for you.
I played 1v3 AI on hard and hardest difficulties. After two hours of gameplay each, the maximum number of villagers each built was between 60-70 villagers for a total of 180-210 villagers. The AI will not get them to 300 total villagers (average 100 villagers) because it focuses on combat units and is limited to 200 population per civilization.