This is something I have never encountered in all my years of using Asus routers. But then I also have all of my critical network items (router(s), switch's, WAP(s), servers, etc) assigned static IP Address and I use the address to connect to them. I think the only time I might have used the router. address is on a new/freshly reset router to connect to it the first time but then the IP Address is usually a 192.168.x.x address so it is not that hard to find.
@geniusmusing It sounds like a firmware upgrade redirects IP address access to router.asus.com. I have always used IP addresses directly for any in-network access. Apparently, #Asus did not consider how this requirement plus #HSTS would interact.
My entire network is offline right now (other than some phone hotspotting during this extended move), but I now intend to do all my network config from a #RasPi that is only used for in-network management tasks.
@lnxw48a1 What I think it is actually doing is a preset static DNS entry pointing to itself because most non tech people can type an address that is words but numbers seem to confuse them. Also, most people only have a single router/internet connection. I checked the router. address and I got "Unable to connect" because I am using my two routers as AP's and have a non asus router.