It’s not inconceivable that the OS memory got corrupted. Factory reset would probably fix it. I’m not sure why you think it’s to be used only as a method of last resort.
I'm also quite certain that a factory reset would fix it but it's a last resort because I'm a fool who doesn't backup their phone regularly.
Maybe I'll have this phone as an expensive paperweight and hopefully if technology advances enough in the future to be able to pull data from it or find out what's wrong, I can grab my sentimental data on there.
