Fix: Unreal GameplayTagContainer Not Replicating

You set a tag on the server. The client doesn’t see the change. The actor replicates other properties fine. GameplayTagContainer is a USTRUCT and follows normal replication rules — but it’s easy to skip a step.

The Symptom

Server-set GameplayTags don’t appear on clients. RPC calls work; other replicated properties update. Only the tag container is silent.

The Required Pattern

// Header
UCLASS()
class AMyActor : public AActor
{
    GENERATED_BODY()
public:
    AMyActor();

    UPROPERTY(ReplicatedUsing=OnRep_Tags, BlueprintReadOnly)
    FGameplayTagContainer Tags;

    UFUNCTION()
    void OnRep_Tags();

    virtual void GetLifetimeReplicatedProps(TArray<FLifetimeProperty>& Out) const override;
};

// Cpp
AMyActor::AMyActor()
{
    bReplicates = true;             // MUST
    SetReplicateMovement(true);       // optional, for transform
}

void AMyActor::GetLifetimeReplicatedProps(TArray<FLifetimeProperty>& Out) const
{
    Super::GetLifetimeReplicatedProps(Out);
    DOREPLIFETIME(AMyActor, Tags);
}

void AMyActor::OnRep_Tags()
{
    UE_LOG(LogTemp, Log, TEXT("Client saw tags update: %s"), *Tags.ToString());
}

Three things must all be true:

1. Actor bReplicates = true.
2. Property tagged Replicated or ReplicatedUsing.
3. Registered in GetLifetimeReplicatedProps.

Mutating from the Server

The container only replicates when modified on the server (HasAuthority). Client-side AddTag/RemoveTag never propagates — the change exists only locally and is overwritten on the next server replication.

void AMyActor::ServerAddTag(const FGameplayTag& Tag)
{
    if (!HasAuthority()) return;
    Tags.AddTag(Tag);
    OnRep_Tags();   // also fire locally on the server
}

Conditional Replication

To replicate to only some clients (owner, relevant), use COND parameters in DOREPLIFETIME:

DOREPLIFETIME_CONDITION(AMyActor, Tags, COND_OwnerOnly);

Verifying

Network Profiler (Window → Developer Tools → Network Profiler) records replicated properties per actor. Trigger a tag change on the server; the property should appear in the next replication batch with a non-zero size.

Or simply Print on the client’s OnRep_Tags. Should fire on every server-side change.

“bReplicates. Replicated. DOREPLIFETIME. OnRep for client reactions. Tags arrive.”

Related Issues

For multiplayer spawn replication, see spawner replication. For input modifier stuck, see input modifier.

Three switches. Tags propagate.