Isle of prayer fire stone drop bugged? lineage 2 3rd class

I did a test twice.

I was farming in Isle of Prayer monsters and during 1 hour. During that time I received 6-8 A grade weapon parts and few dc/tallum common items. But only 1 Fire Stone during that time. The problem is that Fire Stone drop rate is higher ~10 times than those A weapon parts or common items (FS drop ~0.13%, A grade weapon part/common armor ~0.016%)

So where is logic here? Something wrong with Fire stone drop out there... I remember clearly back in your x5/15 GF servers, even if IoP was full of people you could still get 30-40 Fire Stones in ~10-14hour farm (~2-3 stones per rebuff).