Ok, first of all, English is not my native language, that's why you are about to face bad grammar and many typos, so brace yourself, you have been warned. :) Also, I'm not sure this is correct section for posting (possible) bugs, but will shoot anyway. If there is more appropriate place for posting bugs, some good moderator can move that post there.

That bug report is about Souldrinker Epic/Force/Demonspawn. He apply 2 Bombs with hes A3 that detonate after 3 turns. Hes A1 reads as follow:

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Razing Hand [ATK]
Attacks 1 enemy. Decreases [Bomb] debuff detonation countdowns by 1 turn.

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If you equip him with Retalation set, he apply Bomb debuff to someone and then that enemy attack trigger counterattack and Souldrinker retaliate, the bomb debuff do decreases remaining cooldawn as hes A1 states, but then bomb doesn't make any damage. I tested this behavior several times in various dungeons and many arena battles and every time when he use his A1 from triggered counterattack the result is the same. There is no difference if bomb detonate right after hes counterattack or turn or two after - they never produce any damage.

If Souldrinker, equiped  with Retalation set, make normal/regular  A1 attack on enemy with Bomb debuff, there is no problem and all works as intended no matter of hes equipment.

According to Counterattack description, there is no indications that this is normal behavior:

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Counterattack

When attacked, the Champion with this buff retaliates against the attacker using their Default Skill which inflicts 75% damage. Counterattack once when attacked with a multi hit skill. Does not counterattack in response to the enemy’s counterattack. Does not count as a Turn.

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I haven't tested him with Avenging set and can't provide any feedback about that.