The iPhone 5s represents several firsts for Apple and the smartphone industry in general. Not only does the device feature 64-bit architecture, but the latest iPhone integrates a fingerprint sensor and independent M7 motion coprocessor. With new technology there's always the potential for bugs to surface after the latest hardware gets into the hands of users everywhere.
Of course the iPhone 5s is no different, and while reviews have been overwhelmingly positive some users have reported problems. Complaints and issues can always be brought to Apple's attention either in iPhone support communities or at the retail store Genius Bar. Besides troubleshooting, keep in mind the iPhone 5s comes with a one-year AppleCare warranty. Usually devices can be repaired or replaced in-store.