How to permanently fix a periodic, frequent loss of network connectivity under iOS 8.1.x on iPhone?

Ever since upgrading my iPhone 5S from iOS 7 to iOS 8, I experience frequently (usually once a day) a complete loss of internet connectivity, both via Wifi and LTE (T-Mobile). The only workaround is to reboot the phone. I have already tried deleting all network settings, and in upgrading to iOS 8, I set up my iPhone as a new phone. I have an iPad Air 2 also running iOS 8.1.3 that does not have this problem.

Are others experiencing this issue on their iPhones?