Will the Navigation System rebuild when the game start?

I am working on a RTS-Style game, and I want to make a Spectator Pawn to control the characters in the battlefield. I refer to the StrategyGame example and i’ve created the SpectatorPawn.
My Problem is when the game started, the characters i choose can not go to the place where i hit. But after about 30 seconds, the characters i choose can move. I think this is because the navigation system is rebuilding(My map is quite huge, it does need some time to build the navigation). The strange thing is when i delete the AGameMode::RestartPlayer(AController* NewPlayer), my character can move when the game start, but it will make my SpectatorPawn can’t scroll.
Help, i have already trapped in the problem for hours. T_T