Lose a turn?
In the third challenge mission, Overgrown, I assigned one character to open the gate, making them unplayable for two turns. After I did this, a heavy walker spawned, stunned a different character, and was taken down by the third due to one of her shooter traits. After this, I didn't get a turn. Two more walkers spawned, and got a turn, bruising the previously stunned character, and I didn't get a chance to do anything about it. I don't know if this is a common problem that other people are having, but I honestly feel like I got robbed of one of my stars (technically two because I had round passes which thankfully worked this time) because I wasn't allowed that turn.