Addressing Recent Stability Issues

I'm pretty sure its multiplicative and not additive :/

Why not take pics of every exp you get before and after the buffs? Becouse i think it goes like this: normal exp: 100, 3x exp= 300 (doesnt matter if it is 3x or + is the same thing). now if you add HS you get 50% more so you need to get the 50% of 300 and thats the extra exp you get: 50% of 300 = 150 so now you get: 450 exp.
Now lets add 1.5, 1.5 its like adding 50% more exp so with this you go have to get the 50% of 450: 225 so now it adds up to : 675. Now if you add the 2x card it would be: 1350. so instead of multiplicative or adding yous calculate it with % its easier to understand it.
1.2= 20% more (familiar buff), 1.5 = 50% (like hs). Well that is how i understand it