I made an initial post over on Reddit: reddit.com/r/unrealengine/comments/rxro46/niagara_loading_hiccup_on_oculus_quest_12/
TLDR: Any time I try to render what seems to be a very simple and optimized Niagara effect on Quest 1 or 2, the game freezes/chokes up for anywhere from 0.2s - 1s depending on the amount that get loaded and how complex the system is. This only happens on the very first render of a Niagara Particle for that play session. After the initial load, my frame rate is buttery smooth and loading more of that Niagara Particle is no problem at all.
I’ve tried loading them off-screen and async loading, but neither option helped.