I am rendering a volume with a particle system(rendering as mantra points) and it give me flickering only when I render volume and particle together.

When I render only each element, it doesn't do the flickers.

Here goes the example video clip. (see the bottom part of the particle

I've tried matte volume but also gives me flicker, instancing simple geo instead of using mantra point for render also gives me flicker.

Used higher resolution for depth map shadow, but still gives me flickers.

What could cause this?