I wrote a particle spark system some time ago, and since then using shadowmap started causing flicker whenever the particles are emitted;
The effect itself is essentially small neon trail parts coupled with a pointer object, and a tracer part being destroyed right near them. ALL trails have light emission set to 1 and particles generally hover between 0 and 1.
It happens both in studio and ingame, and is not affected by the trails inside of the sparks (deleting them changes nothing, there is basically nothing able to emit light to the shadows aside from trails, and disabling the particles fixes it every time)
Windows 10 home/pro, and a 970 and a 750 Ti (i had both windows editions and cards, all of which had the same issue)
Assets used for the effect:
items.rbxm (6.7 KB)