The key to this mystery is that the unproductive blueberry bush is in a container - a galvanized container that absorbs heat. Blueberries love cool, moist roots and my best guess is that the unusual warm and dry spell we experienced in early June is to blame for the lack of berries. The plants in the ground were better able to cope but the potted plant most likely dried out and suffered from the hot sun hitting the metal pot. June is a crucial time for berry formation. Perhaps in the fall you can transplant the potted blueberry into the ground. After five years in a container the berry bush has most likely filled that galvanized pot with roots so it will dry out quickly. Plants in the ground are better able to weather a change in temperatures.  Keep Growing, Marianne Binetti