Quick answer: Unreal Iris replication bandwidth spiking when 100+ actors spawn in one frame? Iris batches per-frame but unbounded - throttle via Iris.MaxBandwidthPerSecond or stagger spawns.
Wave starts; 200 enemies spawn at once. Server uplink: 8MB for 200ms. Players see lag spike.
Throttle Iris bandwidth
net.iris.MaxBandwidthPerSecond 500000Cap to 500KB/s. Iris queues excess; large spawn waves smooth out over multiple frames.
Stagger the spawn
Spawn 10 per frame for 20 frames instead of 200 at once. Visually identical; bandwidth-wise night and day.
Use Replication Frequency tiers
Distant enemies don't need 30Hz. Tier by distance: 5Hz beyond 100m, 30Hz close. Iris handles the tiering via priority.
“Iris is a scheduler. The scheduler obeys budgets if you set them.”
Build a bandwidth dashboard with per-actor-type attribution. Spawn waves are obvious in the data; the fix follows.