I’ve also confirmed this same result through editing the plugin and logging the sessions results array, then forcing bUsesPresence and bUseLobbiesifAvailable to be true before calling Join Session, and it seems to work fine if they are both forced to true (so the joining logic itself still seems to function as expected if it can get past the initial conditional check).
https://github.com/EpicGames/UnrealEngine/blob/1308e62273a620dd4584b830f6b32cd8200c2ad3/Engine/Plugins/Online/OnlineSubsystemSteam/Source/Private/OnlineSessionInterfaceSteam.cpp#L859C1-L864C3
I think this may also align with the following changes in UE 5.5:
- Deprecated usage of SEARCH_PRESENCE in OSS Sessions
- Fix for override of the value the bUsesPresence in OSS EOS Lobbies
On the first point, Visual Studio logs the following warning when building the plugin source:
warning C4996: 'SEARCH_PRESENCE': SEARCH_PRESENCE ("PRESENCESEARCH") is deprecated and will soon stop being a valid UE-defined key. Please consult upgrade notes for more details Please update your code to the new API before upgrading to the next release, otherwise your project will no longer compile.
I’m not entirely sure what the replacement is supposed to be and the upgrade docs mentioned don’t seem to referenced anywhere in the release notes for 5.5.
The second point suggests to me Epic were aware of issues to do with presence and lobbies from recent engine changes and have made some fixes to EOS accordingly for the 5.5 release, but seemingly have missed something with the Steam implementation.