I had this same issue. The power button on the remote worked, but no others. Unplugged the power cord from the back of the tv. Waited 30 seconds, then plugged it back in. Voila! After the tv booted up, the remote was, once again, fully functional.
Just remember that each Television manufacturer licenses the Amazon app and modifies that app to work with their hardware. I have found that my ViZio Fire TV is so brain dead that I am using the firestick to have the full Amazon Fire capability. In addition to not supporting the DVR capability via Amazon's Recast Box, other features of the interface are just different enough or lack capabilities that I do not use it at all. Amazon is not responsible for updates to the Television firmware and emails to Toshiba should be the vehicle to get resolution on this topic.