Quick answer: Unreal Iris client receiving replication data for actors that aren't in their streamed world? Sub-level loaded server-side but not client-side - replicate level visibility.
Server has Level_Cave loaded; client doesn't. Iris sends Cave-resident actor updates; client errors.
Replicate level visibility
Per-client Streamable Levels list. Server filters replication by what the client has loaded.
Or use Iris world subsystem
Iris's per-client world subsystem tracks loaded levels. Filters automatically.
Verify with NetProfile
Per-actor replication info. Out-of-world actors visible; the bug source.
“Streaming and replication interact. The interaction needs configuration.”
If your game uses streamed levels with multiplayer, the interest management story is its own design doc. Plan it.