The build is pushed to Steam, my friends and I downloaded it and tested on our own individual accounts, which are all added to Steamworks. We are located in the same city. In version 5.5, everything works fine with the same setup. However, in version 5.6, even a clean project with just the multiplayer setup doesn’t work. The dedicated server seems to function properly — the problem persists only with listen servers, according to discussions in the Unreal Discord.
Again, session creation works fine, and traveling to the level as the server also works correctly. Clients can find and see the sessions, but they cannot join — error logs were included in my previous message.