None pawn after postlogin event

Im not sure if i understood you right,

there is a flag you can setup in the game mode to enable spawn or disable spawn of default pawn after post login.
i prefer opening the Game Mode class and looking for the virtual functions you can override

The RestartPlayer in example is needed to override player spawning…

void ASGameMode::RestartPlayer(class AController* NewPlayer)
{
	// ...
 
	/* Look for a live player to spawn next to */
	FVector SpawnOrigin = FVector::ZeroVector;
	FRotator StartRotation = FRotator::ZeroRotator;
	for (FConstPawnIterator It = GetWorld()->GetPawnIterator(); It; It++)
	{
		ASCharacter* MyCharacter = Cast<ASCharacter>(*It);
		if (MyCharacter && MyCharacter->IsAlive())
		{
			/* Get the origin of the first player we can find */
			SpawnOrigin = MyCharacter->GetActorLocation();
			StartRotation = MyCharacter->GetActorRotation();
			break;
		}
	}
 
	/* No player is alive (yet) - spawn using one of the PlayerStarts */
	if (SpawnOrigin == FVector::ZeroVector)
	{
		Super::RestartPlayer(NewPlayer);
		return;
	}
 
	/* Get a point on the nav mesh near the other player */
	FVector StartLocation = UNavigationSystem::GetRandomPointInRadius(NewPlayer, SpawnOrigin, 250.0f);
 
	// Try to create a pawn to use of the default class for this player
	if (NewPlayer->GetPawn() == nullptr && GetDefaultPawnClassForController(NewPlayer) != nullptr)
	{
		FActorSpawnParameters SpawnInfo;
		SpawnInfo.Instigator = Instigator;
		APawn* ResultPawn = GetWorld()->SpawnActor<APawn>(GetDefaultPawnClassForController(NewPlayer), StartLocation, StartRotation, SpawnInfo);
		if (ResultPawn == nullptr)
		{
			UE_LOG(LogGameMode, Warning, TEXT("Couldn't spawn Pawn of type %s at %s"), *GetNameSafe(DefaultPawnClass), &StartLocation);
		}
		NewPlayer->SetPawn(ResultPawn);
	}
 
	if (NewPlayer->GetPawn() == nullptr)
	{
		NewPlayer->FailedToSpawnPawn();
	}
	else
	{
		NewPlayer->Possess(NewPlayer->GetPawn());
 
		// If the Pawn is destroyed as part of possession we have to abort
		if (NewPlayer->GetPawn() == nullptr)
		{
			NewPlayer->FailedToSpawnPawn();
		}
		else
		{
			// Set initial control rotation to player start's rotation
			NewPlayer->ClientSetRotation(NewPlayer->GetPawn()->GetActorRotation(), true);
 
			FRotator NewControllerRot = StartRotation;
			NewControllerRot.Roll = 0.f;
			NewPlayer->SetControlRotation(NewControllerRot);
 
			SetPlayerDefaults(NewPlayer->GetPawn());
		}
	}
}

hope that helps…
Checkout this great tutorial… helped me a lot!