Resetting the vehicle (restart race) causes exaust particles to stay where the car was resetted, it doesnt happen always maybe 1 in 5
I assume the car doesnt fully get destroyed and replaced by another when resetting. Or isnt just moved and repaired, its more of a in place replacement meaning its still in the same prefab world. But when resetting anything parented to the prefab will stay where it got resetted and spawned again with the repaired car, so its duping entities. I cant prove this but I think invisible stuff like probes might be left behind/duplicated too when you reset. (Anything that has a hierarchy component set to the car)