had same experience… Roku 4400X ultra 4 that worked fine for many months with micro SD Sandisk then one day just simply stopped working. System froze on Home Screen, would not recognize or pair remotes. Did everything everyone suggested. New batteries, unplugged/reboot, reset, full system reset including TV reset to factory in case my software somehow was an issue. Smart TV would not even recognize I had a Roku device connected. Spent hours doing this and on line researching my situation.
Then finally I removed my Card powered system off and on…Boom Home Screen popped on and paired immediately. With my newly ordered Roku rechargeable remote. Oh and yes it did pair with my old remote too. I checked !!!
Bottom line is that clearly there is an issue with SD cards and Roku devices. Save yourself time, money and frustration - just pull your SD Card and reboot. surprised and disappointed that Roku doesn’t list this as a known issue. Would save us consumers endless hours of frustration. Goes straight to consumer satisfaction.