A Niagara system on dynamic bounds is culled by its own box, so an explosion vanishes as the camera pans and a trail disappears when its spawner leaves the frame. It tends to show up in a packaged build rather than in the editor.
The engine’s validator checks that fixed bounds exist, not that they are right, and Set Fixed Bounds samples whatever single frame is on screen when you press it.
Niagara Bounds Solver plays every system headlessly one tick at a time, takes the union of the local bounds over every tick a particle was alive, and writes that union as FixedBounds with an optional pad. It draws the old box against the measured one to a shared scale. Preview is the default, every write is journalled so it can be reverted, and a system it cannot honestly simulate is reported as skipped and left alone.
UE 5.8, Win64. The code is AI generated. $19.99 on itch.