What causes an Unreal OnRep function not firing on the listen server?

RepNotify callbacks only run where the property arrives over the network, so the authoritative server sets the value directly and skips OnRep on the listen server's local player.

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 RepNotify (OnRep) Not Firing on the Listen Server

Quick answer: Manually call the OnRep_ function on the server right after you change the property, or move shared logic into a function both paths invoke.

In Unreal, a property marked ReplicatedUsing only triggers its OnRep on receiving clients. On a listen server the host is authoritative, so its own pawn never gets the callback unless you call it yourself.

How to fix it

1. Call OnRep on the server explicitly

After assigning the replicated value on the authority, invoke the notify directly: Health = NewHealth; OnRep_Health();. The engine will still fire it automatically on remote clients.

2. Factor visuals into a shared function

Put mesh, FX, and UI updates in a helper that both the server's manual call and the client's OnRep invoke, guaranteeing identical results on every machine.

3. Confirm GetLifetimeReplicatedProps

The property must be registered with DOREPLIFETIME in GetLifetimeReplicatedProps, and the actor's bReplicates must be true, or the value never replicates at all.

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.

Reproduce it once with full context and the fix writes itself. The hunt is the expensive part.