What causes Unreal replication not working?

The actor or property is not flagged to replicate, you are changing it on a client instead of the server, or RPCs are being called from the wrong authority — replication only flows from server to clients.

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 Replication Not Working in Unreal Multiplayer

Quick answer: Set the actor to Replicates and mark variables Replicated with GetLifetimeReplicatedProps, change state on the server (HasAuthority), and use the correct RPC types for the direction you need.

Multiplayer state that updates locally but not on other clients almost always breaks one of replication's rules: replicate the actor and variable, and only change it where you have authority. Here is how to wire it correctly.

How to fix it

1. Enable replication on actor and variables

Set bReplicates true on the actor, mark each variable Replicated, and register them in GetLifetimeReplicatedProps for C++ (or tick Replicated in Blueprints). Unmarked state never travels.

2. Change state on the server

Replication flows from server to clients. If you set a replicated variable on a client, only that client sees it. Make the change inside a HasAuthority check or via a Server RPC.

3. Use the right RPC direction

Server RPCs run on the server from a client, Multicast and Client RPCs run the other way. Calling the wrong type from the wrong place silently does nothing. Match the RPC to the authority and target.

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.