In POS failed mintings are normal, one way to decrease the number that fail , is to use coin control
and combine the smaller amounts into a larger amount.
If you look at your chart everything that was over 13 interest minted, and most everything with under 1 interest failed to mint. We called it Dust when the amount are too small to mint.
So combining the dust (smaller amounts) together for minting will increase the chance of minting.
Fyi: Coin age does reset when you combine the smaller amounts.