Drop rates of 1* purple/gold talisman evo runes is bugged??

I'm currently running level-1 of BNW to complete the achivements of the current event, but also trying to farm some 1* evo runes (i feel is quite dumb that 1* are harder to get than 3*).

I'm getting tons of red/green/blue 1* runes. But 1 got only a handful of 1*purp/gold. It's weird, becouse I see 2* purp/gold runes dropping at level-1 BNW more frequently than 1*. Is it bugged? My inventory is overflowed with 2*/3* runes, but 1* are a pain! They should be dropping in dungeons and other events, these are key to evolve all new talismans from 3* to 4*.