I had this issue about a month ago at my remote cottage when my Rokus suddenly stopped working and I factory reset them trying to fix. I finally called my Internet provider as Roku was no help. They were familiar with the issue as many customers reported the same problem. Turns out an update pushed from Roku broke Internet connectivity for devices connected to some regional Internet Service Providers (ISP), like mine here on Virginia's Eastern Shore. My ISP had already worked with Roku on a fix. I provided my Roku device IDs to my ISP, they sent them to Roku, and a day later I did a software update to get the fixed update. The "catch" was I had to transport my devices and connect them to another ISP not affected by the original update. In my case I took them to Norfolk and connected them to my Cox network at home. You may be able to achieve the same result if you have a mobile hotspot on your phone and connect the Roku to that network. Then try to register and do an update. I was unable to use the mobile hotspot method as I have no phone service at my cottage location.
Best of luck,
Eric
