What causes duplicate projectiles from predicted and server spawns?

The client predicts a projectile locally for responsiveness and the server independently spawns and replicates its own, with no link between them, so the shooter sees two.

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 Duplicate Projectiles From Predicting a Spawn the Server Also Creates

Quick answer: Tag the predicted object with a client-generated key, and when the matching server-spawned object arrives, adopt it and destroy the local prediction.

Predicting fast actions like shooting feels great, but if the client's predicted object and the server's replicated object are not reconciled, the owning client ends up with both visible at once.

How to fix it

1. Stamp predictions with a unique key

When the client predicts a spawn, generate a unique prediction id and send it with the fire command so the server can echo it back on the authoritative spawn.

2. Adopt the authoritative object

When the server-spawned projectile arrives carrying the matching prediction id, transfer the predicted object's state to it (or hide the predicted one) and destroy the local prediction.

3. Hide replication for the predicting owner

Suppress the normal client-side spawn of the authoritative object on the owner until reconciliation completes, so the duplicate never flashes on screen.

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.

Most of the time the fix is small. Seeing the failure clearly is the part that actually costs you.