What causes an Unreal online session clients cannot find?

The session is created with settings (presence, LAN, subsystem) that do not match what the search query specifies, so FindSessions filters it out and clients never see it.

How do I catch this when it only happens for some players?

Capture it automatically from the player's device with the full stack trace, the device and OS, the build, and a breadcrumb trail of what they did. That turns a vague complaint into a specific, reproducible issue you can fix without owning the hardware it happens on.

How to Fix an Unreal Online Session That Clients Cannot Find

Quick answer: Make the CreateSession and FindSessions settings agree on LAN vs online, presence usage, and the active online subsystem, and ensure both sides use the same build and subsystem.

A session a host creates that no client's search ever returns usually has mismatched session settings between create and find. They must line up. Here is how to reconcile them.

How to fix it

1. Match LAN and presence flags

If the host creates with bIsLANMatch true, searches must also set LAN true, and presence usage must agree. A LAN session is invisible to an online search and vice versa.

2. Use the same online subsystem

Confirm both host and clients run the same active subsystem (NULL for LAN testing, Steam, EOS, etc.) configured identically in DefaultEngine.ini. A subsystem mismatch means they are searching different backends.

3. Align search query with create settings

The FOnlineSessionSearch query settings (and any custom session keys) must match how the session advertised them. A filter on a key the host did not set will exclude the session from results.

Catching the ones you can't reproduce

The hardest version of this to fix is the one you can't reproduce — it only happens on a player's hardware, OS, driver, or save state, under conditions that simply aren't present on your machine. A report that says “it crashed” or “it froze” gives you nothing to act on, so the bug survives release after release while quietly costing you players.

Automatic error capture closes that gap. Each failure arrives with its full stack trace, the device and OS, the build number, and a breadcrumb trail of what the player did right before it broke, so even a failure you have never seen becomes a specific, reproducible issue. Fold identical failures into one signature ranked by how many players each hits, and your worklist sorts itself worst-first instead of arriving as a stream of vague complaints.

This is where a tool like Bugnet earns its place. Its SDK captures every Unreal Engine error automatically with the full stack trace plus device, OS, memory, build, and game-state context, folds duplicates into one grouped issue with an occurrence count, and ties each to the build it first appeared on — so you fix the problem that hurts the most players first and confirm it is gone when its signature disappears from the next release.

Ship the fix, watch the signature disappear from the next build. That's how you know it's really gone.