Replicating a variable in a custom AGameState breaks playercontroller on client

Are you calling the Super for GetLifetimeReplicatedProps?

Such as:

void AActor::GetLifetimeReplicatedProps( TArray< FLifetimeProperty > & OutLifetimeProps ) const
{    
    Super::GetLifetimeReplicatedProps( OutLifetimeProps );
    DOREPLIFETIME( AActor, Owner );
}