Currently emitting & distributing particles along emit time works when time progresses normally. See QQuick3DParticleEmitter::emitParticles() and QQuick3DParticleEmitter::getEmitAmount().

But it is not made to work when user freely moves particlesystem time (say in QDS). For example if timeChange > lifeSpan, particles are distributed too much. Also when time goes backwards, new particles are not emitted.

If this seems to affect performance, consider adding "bool designMode" property or something similar so it could be used in QDS but not affect release performance when not needed. This could be hidden inside QQuick3DParticleSystemLogging. There may come other needs for extra stuff while designing.

Make an testbed example which allows freely animating time (can use SystemPlayPause.qml as a start) but contains also emitter with emitRate and lifeSpan so that particles get reused.