It is possible the dough was kneaded too long. It takes time for gluten to develop fully. Bread dough should be kneaded 4 to 10 minutes. When you have kneaded the dough enough, it will be smooth and elastic, and tacky rather than sticky or dry. A good test is to press the heel of your hand firmly and deeply into the dough; hold it there 10 seconds. If your hand comes away clean, you have kneaded the dough enough.