By any chance, is the one that's not working, single band only (2.4GHz) and the others are dual band models? This would indicate an issue with 2.4GHz which might have been caused by an automatic router update. (If so, and you check the router, make sure 2.4GHz is enabled and it is set for b/g/n modes, not just g/n modes.)
Other possibilities include a noisy environment and a device failure. Sometimes just moving or rotating a device can help as can changing the Wi-Fi channel.