I have noticed some odd things with harvesting.
Garden- Sometimes I get several percentage points per harvest other times I will get zero for three or four harvests in a row. I could understand the none at level 86 if not for the several on other harvests. This is with Alana Leaf and either the regular or the hasty.
Wild harvests- I have been getting more pieces and gems when I don't use triad potions and herbs than when I do. Also, uncommon supplies yields less products ( though faster) than basic. This is with hat and maxed harvest levels.