Quick answer: Unreal Blueprint NetMulticast event running locally before replication to other clients? Multicast runs on the calling machine first - guard with Has Authority.
Server triggers a NetMulticast spawn explosion; explosion happens twice on server (once local, once 'from network').
Guard with Has Authority
if (HasAuthority()) {{ ... // server only ... }}Skip server-side execution in multicast; let replication do the work.
Or trigger server-side from client
Client RPC -> server; server emits multicast; clients all see. Server isn't a client.
Audit multicast patterns
Each multicast has authority semantics. Document; consistent.
“Multicast events fire on the originator too. Some intentional; some bug.”
For UI VFX that you want everywhere, multicast is correct. For gameplay state changes, use Run On Server + multicast pattern explicitly.