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Fruit on any plant tends to be more sour or bitter if the plant is not getting enough nutrients or enough water. Since it is a neighborhood wide issue, I would look to the weather. Was it particularly dry this year? If so, the trees may have not gotten enough water. Was it very wet this year? The roots may have been struggling due to a lack of oxygen and did not take up the nutrients it needed, or some nutrients were washed away.

Regardless, the fruit should return to their sweet selves by next year. If you want to hedge your bets on that, fertilize the tree with a balanced fertilizer that contains micro-nutrients as well as the typical NPK balance.