Adding a new particle system increases the SetPass call in one Unity version, but not in another version?

I'm using 2 versions of Unity: 2018.3.14 and 2019.1.9

In both of the versions, I have 2 scenes: Scene A and Scene B.

In scene A (of both Unity versions), when I don't have any particle systems in my scene, the number of SetPass calls is 6. When I add a new particle system, the SetPass call stays at 6 in version 2018.3.14, but increases to 7 in version 2019.1.9. As a matter of fact, no matter how many particle systems I add in Scene A of version 2018.3.14, the number of SetPass calls stay the same (even when all particle systems have different materials), whereas in version 2019.1.9, adding a new particle system increases the number of SetPass calls. Initially, I thought this is probably a change that the Unity developers made for the newer versions of Unity.

Things got weird when I ran the same test in Scene B of both Unity versions. In both of the versions, when I add a new particle system to Scene B, the SetPass call increases. Every time I add a new particle system (with each system having a different material), the SetPass call increases. This applies to both Unity versions.

Why is it that adding a new particle system in Scene A of version 2018.3.14 doesn't change the SetPass calls and adding a new particle system in Scene A of version 2019.1.9 does increase the SetPass calls, where in Scene B of both Unity versions, the SetPass calls increase whenever a new particle system is added?

You might be wondering, "Maybe I did something different in Scene A which is causing the SetPass calls to behave differently". In this case, I should let you know that in both Unity versions, Scene A is my main game scene. It is where I created my game and it contains all the other prefabs (with scripts) in the hierarchy. However, I ran the tests above AFTER deleting all the prefabs so that both Scene A and Scene B are the same. But I got the same results.