Story mission Chapter 1.10 - Enthralling Victor has the challenge “Grounded” which requires a win without using Flying creatures.
I’ve won three times now, without flying creatures each time, and still haven’t received the reward.
Story mission chapter one part 2, 12th mission has the same bug.
Edit: seems to be all “grounded” mission objectives that are bugged.
I noticed the original post was outdated, but I wanted to add my two cents. My mission 1.10 does not have that as an objective. I have: Win the Fight! Resilient (take 10 or less damage) and Speed (win in 10 or less rounds)