Quick answer: Unreal Niagara mesh particles compiling shaders at first spawn despite PSO precompile? Particle mesh renderer's shader variants not in the bundled PSO list - add explicit.
First boss explosion: 200ms hitch from mesh particle PSO compile.
Add to bundled PSO
Niagara System > Bundled PSO > includes mesh renderer variants.
Or warm up at boot
Spawn a hidden VFX at boot; PSO compile during loading screen.
Use PSO cache stats
stat psocache. Per-frame compile count visible; first-spawn hitches diagnose.
“PSO precompile is per-variant. Coverage requires explicit inclusion.”
Audit your bundled PSO list. Each used variant should be present; missing = first-spawn hitches.