I chatted with Amazon help and they suggested I reset my TV (Insignia) to factory settings. That I tried, but then my TV remote wouldn't work to complete the setup. I contacted Insignia help, and they informed me that a software update is why the TV would no longer power up to last input. She said that it should be fixed with the next software update. After assisting me to get the TV and remote to reboot to factory settings, the last input worked again. I assume because the software updates were wiped out with the reset. I do not know if the TV goes out and looks for updates, or if new software is pushed to the TV when it becomes available. Anyway, my last input works again - for now.
Success!!! As reported on a similar thread, software has been pushed out and the last-channel start up is functioning again. Thanks to all who raised the issue and to the tech(s) who fixed the problem.