Login using Nighthawk App on iPhone7 fails with white screen

I recently updated my iPhone7 to iOS 15.8.4.  I shutdown power to my internet modem and Nighthawk X10 AD7200 WiFi and LAN Router (running V1.0.5.42 firmware) in order to perform electrical maintenance.  Upon work completion I successfully rebooted both internet modem and router and verified proper operation to both LAN and WiFi connected devices.  I have control of the router accessible and functional from my desktop connected on LAN.  However, when I attempt to start the Nighthawk App on my iPhone7, the App opens what looks like what might be an internet browser window that is completely white and featureless.  I have rebooted the iPhone7 with no improvement.  I have completely removed and reinstalled the Nighthawk App but this did not alter the failing behavior.  As such, I cannot use the Nighthawk App.  I assume that the Nighthawk App has failed due to security changes made during the iOS upgrade to 15.8.4.  Please help.