After full level on her midnight ritual the cooldown is not 2 as you wrote ( two times minus 1 turn from 4) but still 3. I wasted my red tomes on her!! This is a huge problem. I also made a ticket. 

I play apple IOS 11.3. But you just forgot to apply the right cooldown in your server programming. It’s your mistake not mine. The 2 cooldown is crucial for Serris and I have two of them