KOH shouldn't go stale, but it will absorb water right out of the air. If the flakes are wet or sticking together, it's no good!
I used ASM for a while leaving my KOH that was already 18 months old, in a mango chutney container with a screw top. I went back to KOH and it was fine. I've had as little as 6% drop out after the first stage (2 stage no-titration).
Assuming that your KOH is okay, i'd guess it's as Paul says, you've got to look at the dryness of your feedstock or meth.