How to Fix Server-Spawned Objects Appearing Twice on Clients

An enemy or pickup that appears twice on clients but once on the server is being created in two places: by replication and by local client code. Spawn only on the server. Here is how.

How to fix it

1. Spawn only on the authority

Call the spawn API (NGO's NetworkObject.Spawn(), Unreal's SpawnActor on the server, Godot's authoritative add) on the server only. Replication then creates the client-side copies automatically.

2. Remove client-side Instantiate

Delete any client code that locally instantiates the networked prefab. The replicated copy already arrives from the server; a local Instantiate on top of it is the second object.

3. Use spawn callbacks for client setup

If clients need to configure the spawned object (attach effects, set materials), do it in the network spawn callback on the replicated instance rather than by creating a new object.

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 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.