CreateAdvancedSession Works, But Can't Find or Join from Another PC (UE5.5 Steam OSS)

I’m working on a multiplayer game using Unreal Engine 5.5 and the Advanced Sessions plugin with the Steam Online Subsystem (AppID 480). My setup works correctly in many areas: sessions are created successfully, Steam initializes properly, player names display, and the overlay works. I’m using CreateAdvancedSession with UseLobbiesIfAvailable, bShouldAdvertise, and bUsesPresence enabled, and I added a custom session tag (GameTag = TuniGamesHub) using the ExtraSettings array. I filter by the same tag in FindAdvancedSessions. However, I’m facing several issues: (1) a ghost session always appears with 16 slots and returns “outdated” when joining, even before creating any session; (2) real sessions I create on one PC never appear on another, even with matching builds and filters; (3) Steam invites can be sent and received, but the invited player does not join the session or trigger any join logic. I’m still using OpenLevel("MapName?listen") for travel, as shown in most tutorials. I’ve configured DefaultEngine.ini correctly with SteamNetDriver, the correct connection class, and verbose logging. Seamless travel is enabled in the GameMode. Both Steam accounts are from the same region, so region-locking is not the issue. I’m looking for help confirming that my session setup is correct and understanding what could be causing the session discovery and invite system to fail.