Its not a bug , u just didnt clear the debuffs

Gaara [Swimsuit]

At the beginning of every round, causes unavoidable small damage and Discouragement to up to 4 units in the opponent's lineup.

Debuff Discouragement: Units suffering from this Debuff cannot receive additional Buffs and Shields. Lasts until the end of the next round or

until that unit executes a Mystery. Discouragement is Irremovable and neglects Immunity.

In your situation, 4 units of ninjas have the debuff discouragement. To remove the debuff you need to use 1 mystery for that unit. Basically only Yagura use myst so the immunity buff that you copied only got applied to Yagura whereas the other 3 nin with discouragement debuff cannot receive the immunity buffs.

Because you didn't clear the discouragement debuff

Other Element Nature Training

- Yagura copy the ninja

>Unit 1 = Gain Immunity 2 Rounds Buff

>Unit 2 = Gain Immunity 2 Rounds Buff

>Unit 3 = Gain Immunity 2 Rounds Buff

>Unit 4 = Gain Immunity 2 Rounds Buff

Wind Element Nature Training

-Gaara Swimsuit does his trigger, causes unavoidable small damage and Discouragement to 4 units

>Unit 1 (Discouragement) =

>Unit 2 (Discouragement) =

>Unit 3 [Yagura] (Discouragement) =

>Unit 4[Clone] (No Debuff) =

>Unit 5 (Discouragement) =

- Gaara Swimsuit only hits 4 units

- Yagura uses myst to copy the ninja

- Because Yagura use myst, the discouragement debuff on him only got cleared

>Unit 1 (Discouragement) = Because discouragement, no buff can be gain

>Unit 2 (Discouragement) = Because discouragement, no buff can be gain

>Unit 3 [Yagura] (No Debuff) = Gain Immunity 2 Rounds Buff

>Unit 4[Clone] (No Debuff) = Gain Immunity 2 Rounds Buff

>Unit 5 (Discouragement) = Because discouragement, no buff can be gain

If Unit 1 use myst , Unit 2 use myst, then followed by Yagura myst

>Unit 1 (No Debuff) = Gain Immunity 2 Rounds Buff

>Unit 2 (No Debuff) = Gain Immunity 2 Rounds Buff

>Unit 3 [Yagura] (No Debuff) = Gain Immunity 2 Rounds Buff

>Unit 4[Clone] (No Debuff) = Gain Immunity 2 Rounds Buff

>Unit 5 (Discouragement) = Because discouragement, no buff can be gain

Hope you understand~

If your talking about why we can have immunity 2 rounds, its been there for long time. Don't think its a bug but maybe is intended to at least help players to clear the level. Not guaranteed to clear even if you copy to get the buffs thou. Especially in Wind NT, need some strategy if your using yagura copy way. Also, not sure you noticed but other elements have same mechanics, Earth and Fire NT have someone who gives immunity too.

NT rankings nowadays wants you to use all same counter element to get maximum pts. So using Yagura to copy at other element stages is not optimal but at least helps you get some pts. This mode have been here for a long time, just this time the mobs changed. Old ones also have someone who gives immunity and nothing done to fix there (if it's a bug).

Not sure about CN but Yagura copying is still doing what he does, copy opponents and get their passives. Working normal as it should.