Hello. We were having the same issue on 5.3.2 (can find/create/join and play) in a Development package uploaded to Steam, but unable to join sessions using a Shipping build (albeit still being able to create and find sessions).
We are using the Advanced Sessions plugin, lobbies and no Steam Sockets, and were unable to join the created sessions (server travel failed and sent us back to the Main Menu, and only in Shipping builds).
Overriding these console variables / system settings fixed the issue for us, at least for now.
this is what our DefautEngine.ini looks now:
[/Script/Engine.GameEngine]
+NetDriverDefinitions=(DefName="GameNetDriver",DriverClassName="OnlineSubsystemSteam.SteamNetDriver",DriverClassNameFallback="OnlineSubsystemUtils.IpNetDriver")
;+NetDriverDefinitions=(DefName="GameNetDriver",DriverClassName="OnlineSubsystemEOS.NetDriverEOS",DriverClassNameFallback="OnlineSubsystemUtils.IpNetDriver")
[OnlineSubsystem]
DefaultPlatformService=Steam
;NativePlatformService=EOS
[OnlineSubsystemSteam]
bEnabled=true
SteamAppId={insert your steam app id}
SteamDevAppId={insert your steam app id}
;SteamShippingId={insert your steam app id} (not sure if this one actually gets used lol)
bInitServerOnClient=false
bUseSteamNetworking=false
[/Script/OnlineSubsystemSteam.SteamNetDriver]
NetConnectionClassName="OnlineSubsystemSteam.SteamNetConnection"
[SystemSettings]
net.CurrentHandshakeVersion=2
net.MinHandshakeVersion=2
net.VerifyNetSessionID=0
net.VerifyNetClientID=0
[ConsoleVariables]
net.CurrentHandshakeVersion=2
net.MinHandshakeVersion=2
EDIT: There was also something else that was interfering in the Shipping builds.
On previous testing versions, we were using Epic’s EOS.
Apparently, this triggered some changes in this setting file:
C:\Users{User}\AppData\Local{YourGame}\Saved\Config\Windows\Engine.ini
If you’re doing a clean install of the Game, the {YourGame} folder will be created with this file, and only a few [Core.System] Paths will be written.
The file we had been using had some NetDriver settings (I don’t know why) that were tampering with the Create/Join flow.
Deleting the entire folder finally fixed this issue. And now, after playing a few times, the only settings that are modified/added automatically during gameplay is the following:
[GameNetDriver StatelessConnectHandlerComponent]
CachedClientID=4
which doesn’t seem to have any influence on how the game runs.
So, if you’re having the same issue as us, before attempting any fix, check if this Engine.ini file has any Subsystem/NetDriver settings written, because if it has, then those settings will be interfering with the settings you used to create your Shipping package