I have 3 X Gigabyte RX570. All 3 cards are same and have same gpu/memory clock settings. Why 2 of them give constant 23 MH/s and one 21 MH/s. Temperatures are under 60C on all cards.
Get used to it since its just really normal to have different MH/s on any gpu you do have sometimes they are similar but mostly based on my experience they are different in numbers but they do have the same configurations. The gaps aren't too far which I considered it as a normal thing unless if they gap for almost reaching out -10 then there would really be a problem in that case.