Hi, when you can set your Actor BP_Bomb to replicate and use something like this. The bomb spawning is handled by the server and because the bomb actor is set to replicate every client will see it.
If I would guess whats happening in your setup is you have the BP_Bomb Actor set to replicate. When a client wants to spawn a bomb it’s replicated to all. Therefore it gets once spawned on every client and once on the server. Because the actor is set to replicate the actor you’ve spawned on the server gets replicated to every client, so every client will see two bombs and the server will only see the one it has spawned.