How often did you hill up, and how deep are your grow bags? Reason I ask is because I grew the Yukons two seasons ago, and only got a handful of potatoes.
Did you have potatoes all through the grow bag vertically, or were they all on the same or close to the same level you put the seed potatoes?
I was told we can't grow potatos that make a pyramid-shaped tree underground and grow all along the stem as high up as the vine goes. Our potatoes (because of our seasons) will only produce potatoes outward and on the same level as we set the seed potatoes.
Here's what I used as my vessel (plus two 20 gallon Smartpots)