Yes, sew-in extensions loosen up as they wear out over time. They get displaced and lay loose due to the braids and the sewn thread beneath loosening up. That's normal and does not suggest the installation process was poor.  Some ladies have a false belief that braiding tightly would make the sew-in extensions more durable. In fact, they will not take more time to loosen up, but pain and hair loss will be the aftereffects.