At first I sent this message to @richardkettlewell directly via private messages but he asked to make it public, so here it is. We've recently updated our project form 2017.1.4. to 2018.3.12 (yeah... there were some issues with the versions in between) and everything was great on the first sight. But then I found out that some of the particles are moving with noticeable jitters. Since they use a custom simulation space I'm pretty sure that at some point prior to 2018.3.12 you've changed the moment when that simulation space is taken into account. Specifically, now it's taken into account before LateUpdate, but before that it was done after LateUpdate. I made this conclusion because we're moving the transform used for custom simulation space in LateUpdate. I searched through the changelogs but did not find any mentionings about this change. I wonder is my guess right and if so what was the reason for doing this major change?