It seems like a bug, because it persists even when you add a hold keyframe.
What’s happening is that Particle World is applying a sort of motion blur/frameblend to the particles (you can check by setting the particles’ type to Lines, they’ll become super long for that frame). Particle world obeys the sudden jump in speed (-3 seconds in 1 frame) but like I say, it doesn’t obey even if you add a hold keyframe that the timing should stay still).
I’ve found another fix though: in your CC Particle World precomp’s comp settings enable “Advanced -> Preserve framerate when nested or in render queue”