Hello,
Please, review your process to upgrade the skill up. It's a waste of time, energy and money the process of upgrade the skill up.
In my case, I tried for two times upgrade the skill of Hayyel and two times gave my failed.
The first time I tried with 5 green imps (75%) and just now I tried with 6 green imps (90%) and again the upgrade has failed.
Two times bad luck with high index... your algorithm is wrong.
I know your answer "bad luck" but all your answers to people who have claimed is the same the "bad luck" and It isn't logical