This happened on iOS. I confirmed that it did not happen on PC.
What you were expecting to happen, and what actually happened?
Expected - All troops take 5 damage and the first troop moves to last
Happened - One troop did no take damage and the first troop moved to last
What are the steps to make it happen again?
In a normal game - Was playing quests and challenges
Upon the enemy casting Dervish the enemy begins to deal 5 damage to all friendly troops.
Visual display shows 5 damage on all friendly troops
Upon examination friendly troops have taken incorrect damage. (In my screenshots it shows only 15 damage dealt [5 damage to 3 troops]. Giant Spider has not taken any damage. In other games one troop has taken 10 damage and another has taken 0)
Do you have any screenshots or video you want to share with us so we can see the problem? Attach them to your post!