Apple unveiled a "private address" feature in iOS 14 to enhance security. This feature tells the device to use a different, random MAC (media access control) address for each Wi-Fi network it connects to. By default, the private address feature is enabled on devices running iOS 14 or later.
This creates a problem on networks like ResNet WiFi because registered devices are identified by their MAC address. If your device chooses a different MAC address the next time it connects, you'll be asked to re-register.
Fortunately you can disable the private address feature by going to Settings -> Wi-Fi -> ResNet WiFi:
It's a good idea to turn off the private address feature for ResNet WiFi, BearNet and BearNet Secure to avoid having to re-register your device.