I personally do not have a direct experience to link a product failure but there are some common reasons for the failure to occur. The device can experience some form of contamination whether it is from a chemical attack or foreign substance. Poor molding of the device is another reason that can lead to a deform before the device reaches final assembly and it is the usually cause for device failure. Next, the manufacturing/ assembly QC and poor product design creating difficulty re-creating the device based on the documentation and expectations from the design phase and having that be pushed into the manufacturing floor. Also, Overstress or stress overload to the device created a stress crack that pushed the device into the failure zone. Lastly, the incorrect material selection is a critical issue that can make or break the device. With the material, it is important to keep in mind the various environments need to be taken into account because it can be a factor to alter the ideal properties for the device to function properly.
http://www.qmed.com/mpmn/article/five-common-causes-medical-device-failure