Quick answer: Unreal Niagara SetVariable on a CPU emitter's spawn rate not applying? CPU emitter caches spawn config per-tick; SetVariable updates next tick - or use SpawnRate parameter.
Set spawn rate to 100 at frame 1; expected immediate burst. Particles appear next frame.
Set on Spawn module
For one-shot rate changes, set via the Spawn module's parameter directly. Applied at the next spawn tick.
Or use SetVariable on User Parameter
User parameters update immediately. Emitter Module reads on next tick; one-tick delay tolerable.
Verify with stat Niagara
Per-emitter spawn rate visible. After SetVariable, the value should match your set.
“Niagara variables are tick-bounded. Set now means seen next tick.”
If spawn rate timing matters, plan the one-tick lag. It's small but visible at low FPS.