Those cards has Hynix memory.
About GPU clock, the mining hashrate for ETH on those cards are very dependable from GPU clock. If I set it to 1100 on example it will mine 24.5 mhs, and they can go up to 26.8 on 1290 (but not stable because of high clock for them).
When you OC cards on Afterburner you must rise power limit, rise it to max and dont worry. When you set GPU clock 1200 but power limit is 0 your card will go 1020 mhz, but if you make Power limit at max, the card will go at 1200 Mhz.
Btw dont rise mem clock so much
Sounds very strange, really, I never met such problems as well as solution you offer. Could it be badly designed VRM or so cheaper manufacturing? I am not too familair with cards design.
Are you using Claymore miner?
Yes I am using Claymore miner.
Yes it is cheaper manufacturing I think. The card use some parts from 470 some from 570. The drivers recognize them as rx 570. Maybe the chip is from 570 but vram from 470. I have few friends with same cards and the same problem they had.
We menaged to make speed a little beter ( 26 mhs ) but it is not power eficient, the sensor shows about 115w (out of wall is more).
Strange is that the cards are marked as MINING but cant mine stable beyond 26-26.6