RAX 120 authentication issues

Not sure if my issue is exactly this. Just this past weekend the network started to have issues. The laptop connected to the router via Ethernet is able to maintain an Internet connection. However, all wireless devices (Apple TV, Sony Bravia 930, HP laptop, iPhones, iPads, Nest) lose Internet access. The devices still show as being connected to the network with full signal strength, but are not able to access Internet content. I am also sometimes unable to connect to the router through the Nighthawk app even though the device shows as being on connected to the network. When I try to access the router inteface through a browser it will throw up a login screen every 30 seconds to a minute and often reject the username and password (even though they are correct and work a few seconds later) and the logs will show a failed authentication. My laptop will also throw an error in every browser saying something like your connection is not private NET::ERR_CERT_COMMON_NAME_INVALID for google.com but then go on to connect after 30-45 seconds.

We have had the ISP check the cable modem and all is fine. So, this seems to be some issue with the router. I've unplugged it and let it sit for 30 seconds or so but that doesn't seem to fix anything. I've not tried a reset or to turn off SmartConnect or AX as of yet. It is running on .90 and I'm not sure when .90 wasa installed on the router.