Hello,
I always use 6 cards to do skill upgrade, however due to the pressure from the limited number of cards, I did 2-times using 5 cards and I lost all very rare hard to find cards in both cases in a row.
5 cards means %82 chance, bad luck chance is %18 but the chance of being bad luck for 2 times in a row is:
0.18x0.18=0.0324
This means either I have been so bad luck that %3 has happened to me, or there is a glitch on your random generator for the skill upgrade.
My main request is to ask the design teams/programmer to re-evaluate the random generator.
Another suggestion helpful to reduce the frustration:
To me, it is not a good idea to increase the limit (350) as it is already very high. however due to increased number of skills, skill upgrade is very frustrating.
Therefore, I suggest stop creating new skill names for the some of similar skills. A good example are 8* evolved dragons from 8* dragons! (it is odd already) with very very very high CP of 35 and worse of all changed name for the same skill and limited boost of leader skill (X2 compared to many other cards that they do x2.5)
Anyways, this new 8* evolved dragons from 8* dragons (Is there a better way to mention them?) is another topic but a new skill name for the same skill for these cards and many other cards makes the 350 limited to be low.