Can't join session with Steam online subsystem sometimes.

[LeeYi-user]

I followed this tutorial to make a multiplayer game via Steam. Everything works fine and I was able to create/join session on two different accounts/pc.
However, sometimes when I try to join a session, it failed. I tried to close firewall or use VPN, but it still fails like 50% of the time. (Create session always work with bUseLobbiesIfAvailable = true.)
Here is my DefaultEngine.ini:

[/Script/Engine.GameEngine]
+NetDriverDefinitions=(DefName="GameNetDriver",DriverClassName="OnlineSubsystemSteam.SteamNetDriver",DriverClassNameFallback="OnlineSubsystemUtils.IpNetDriver")

[OnlineSubsystem]
DefaultPlatformService=Steam

[OnlineSubsystemSteam]
bEnabled=true
SteamDevAppId=480
GameServerQueryPort=27015

[/Script/OnlineSubsystemSteam.SteamNetDriver]
NetConnectionClassName="OnlineSubsystemSteam.SteamNetConnection"

And my C++ function to create session:

void UCPP_GameInstance::CreateServer()
{
	UE_LOG(LogTemp, Warning, TEXT("CreateServer"));

	FOnlineSessionSettings SessionSettings;
	SessionSettings.bAllowJoinInProgress = true;
	SessionSettings.bIsDedicated = false;
	SessionSettings.bIsLANMatch = IOnlineSubsystem::Get()->GetSubsystemName() == "NULL";
	SessionSettings.bShouldAdvertise = true;
	SessionSettings.bUsesPresence = true;
	SessionSettings.NumPublicConnections = 5;
	SessionSettings.bUseLobbiesIfAvailable = true;

	SessionInterface->CreateSession(0, FName("My Session"), SessionSettings);
}

Find session (ignore the funciton name):

void UCPP_GameInstance::JoinServer()
{
	UE_LOG(LogTemp, Warning, TEXT("JoinServer"));

	SessionSearch = MakeShareable(new FOnlineSessionSearch());
	SessionSearch->bIsLanQuery = IOnlineSubsystem::Get()->GetSubsystemName() == "NULL";
	SessionSearch->MaxSearchResults = 150000;
	SessionSearch->QuerySettings.Set(SEARCH_PRESENCE, true, EOnlineComparisonOp::Equals);

	SessionInterface->FindSessions(0, SessionSearch.ToSharedRef());
}

Join session after session found:

void UCPP_GameInstance::OnFindSessionComplete(bool Succeeded)
{
	UE_LOG(LogTemp, Warning, TEXT("OnFindSessionComplete, Succeeded: %d"), Succeeded);
	if (Succeeded)
	{
		TArray<FOnlineSessionSearchResult> SearchResults = SessionSearch->SearchResults;

		UE_LOG(LogTemp, Warning, TEXT("SearchResults, Server Count: %d"), SearchResults.Num());

		if (SearchResults.Num())
		{
			UE_LOG(LogTemp, Warning, TEXT("Joining Server"));
			SessionInterface->JoinSession(0, "My Session", SearchResults[0]);
		}
	}
}

Client travel after join session:

void UCPP_GameInstance::OnJoinSessionComplete(FName SessionName, EOnJoinSessionCompleteResult::Type Result)
{
	UE_LOG(LogTemp, Warning, TEXT("OnJoinSessionComplete, SessionName: %s"), *SessionName.ToString());
	if (APlayerController* PController = UGameplayStatics::GetPlayerController(GetWorld(), 0))
	{
		FString JoinAddress = "";
		SessionInterface->GetResolvedConnectString(SessionName, JoinAddress);
		if (JoinAddress != "")
		{
			PController->ClientTravel(JoinAddress, ETravelType::TRAVEL_Absolute);
		}
	}
}

I know there is already a lot of posts about “Steam online subsystem not working”. But I guess none of them only fail 50% of the time? I want a clear explanation of why this happened. Maybe because of the instability of the internet? Or can I adjust the handshake times? Use TCP instead?

I am using Unreal Engine 5.3.2 on Windows 11. Running packaged build (Development) on both machine. Will be very thankful if someone can help me with this.

[LeeYi-user]

Here is the log when it failed.
Client: SimpleFPS.log (222.6 KB)
Listen server: SimpleFPS.log (155.0 KB)

I think the main error is this (from client when it tries to join session):

[2024.08.21-06.31.52:977][529]LogNet: Error: UEngine::BroadcastNetworkFailure: FailureType = PendingConnectionFailure, ErrorString = Your connection to the host has been lost., Driver = PendingNetDriver SteamNetDriver_2147482478
[2024.08.21-06.31.52:977][529]LogNet: Warning: Network Failure: PendingNetDriver[PendingConnectionFailure]: Your connection to the host has been lost.
[2024.08.21-06.31.52:977][529]LogNet: NetworkFailure: PendingConnectionFailure, Error: 'Your connection to the host has been lost.'

[LeeYi-user]

Ok I finally found the reason why it failed. It is because of the session didn’t get destroyed properly. When I close the game on the listen server, it still shows up in the search results after calling find session. Therefore, It finds 2 sessions before I try to join. And in my code it just joins the first one, which is already dead.

Guess I need to find a way to destroy the session properly or filter the search results.