I think it's just RNG. I had a serious shortage of wind for a while. Now (after spending what I could early, and then making more keys since) it's water I'm shortest on and wind I have the most of. In general it seems the best way to deal with it is to accumulate a lot before you start spending to give you the best chance to correct for it.I am having a serious unbalance in the key colors: about half my keys are red, the others are about 25% each - just bad luck or is there a system to the madness?
My current keys are 34 wind, 24 fire, 17 water.