Usually when your AI won’t move, first thing to check is did you already place nav mesh bound volume in the level? and you have to make sure if the area you want already covered with the nav mesh bound volume. (You can check if the area is walkable by AI easily by pressing P on the Editor, then the green area like in the picture below is the one that walkable)
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Second, you also want to make sure that your spawned AI already possessed with AIController. One way to check this is just by play the game, and check is there any AIController in the level.
If there is no AIController spawned, then you need to check your AICharacter BP. Do you already check auto possess AI for Spawned and Placed in World already?
Make sure the Auto possess AI is set to placed in world or spawned to make your AI possessed by the AIController automatically.