XR500 DNS/Site Issue

I am experiencing a problem with my XR500 router while trying to log into LastPass.  When I enter the full website address, including "www," I am able to access the main page without any issues. However, if I attempt to visit the non-www version of the site, I receive a "connection is not secure" error, with no way to bypass it. Moreover, when I click on any links on the main site that lead to a non-www subpage, such as the login page, I encounter a connection error. This problem affects all devices connected to my network through the XR500 router. The issue does not occur if I access the site through a VPN or proxy, or if I connect directly to the cable modem. Hence, it seems to be related to the router. I have gone through the DNS and site blocking settings on the router, and I have even performed a factory reset, but the problem persists.  I'm lost at this point.