Quick answer: Unreal Niagara event handler firing on a deactivated component? Deactivation queues; events already in flight - check IsActive in handler.
Collision particle deactivated; handler fires for an in-flight collision; references stale state.
Validate in handler
if (!IsActive()) return;Skip handlers for deactivated components.
Or use Reset before deactivate
Reset; deactivate. Events drained; no stale.
Audit handler patterns
Each event handler defensive against deactivation.
“Deactivation is queued. In-flight events handle the boundary.”
If your event handlers reference state, the IsActive guard is mandatory. Document.