According to this screenshot, your own game says that as you earn these resonances, they are supposed to stack. Meaning you add the total of the first, second, and third if you hit all three:
This is incorrect. I have received a 5th yellow accessory, and according to your own rules, I should have had 7 AP + 14 DP added from the 3rd resonance alone. Which means 21 total CP from reaching the last tier, plus the 3 CP I received from an upgraded item (my old +4 Ronard Ring is 44 DP, the Red Coral Ring +0 is 47 DP. So a total increase of 21 CP from resonance and 3 CP from the upgrade, totalling 24 CP.
As you can see by the 2 screenshots above, when I put on the last yellow accessory, I only get 10 CP total. This proves that the buffs do NOT stack like you said they do. I am receiving 3 AP and 4 DP from the difference between tier 2 and tier 3 resonance, not the entire +7 AP and +14 DP that is promised. (3 AP + 4 DP from resonance = 7 CP + 3 CP from upgraded item = 10 CP total)
I would like you to fix this because I have spent some money on accessories because of the new resonance saying it stacked, which means all 3 tiers add together. However as my screenshots show, they do not stack, only give you the extra beyond what the others already gave you.
The buff works correctly, what they mean by stacking is if you have 3 Yellow and 2 Orange Accessiores.
Then you get the bonus of 3 yellow accessiores and the bonus of 2 orange accessiores.
So 2 Attack + 7 Defense and from the Orange 20 Attack + 30 Defense.
Yellow ones don't stack among themselves.
※The Resonance effects stack. For example, equipping 5 Epic Accessories will apply the effects of equpping 2 or more and equipping 4 or more on top of equipping 5 Epic Accessories. For example, the effect from equipping 2 Epic and 2 Mystical Grade Accessory will stack. Equipping all 5 will not stack effects from equipping 2 or 4 accessories of the same grade. (Updated 01/07 07:20 PST)