Okay i found it !
Holy moly it’s been a full week i’m stuck on it.
Whoever see this, i was having the same issue as this guy : AI Controllers dont start
And found this answer on reddit : https://www.reddit.com/r/unrealengine/comments/msds2s/ai_not_working_when_game_is_started_in_a/
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Hey there,Try this :
Go to Edit → Project Settings →
Navigation Mesh →
Runtime Generation from Static to → Dynamic
You are welcome. 
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