I've noticed that certain skills could override your existing names. This happened to me several months ago. I have several Wyze Cams. I enabled the Wyze skill but I almost never use the skill. But if I wanted to look at a particular camera, I would say, "Alexa show me the front door." The company that makes Wyze Cams also make a security system. While my security system is entirely different and from a different company, the Wyze skill intercepted the name of my security system. I used to be able to say "Alexa, arm security system." I would always work. And it has worked for many months prior. Then one day it didn't work. It took me a few days to realize that the Wyze skill did something so that I couldn't call my alarm/security equipment "security system" any more. I think Wyze reserved "security system" for itself, even though I don't have a Wyze security system. Since I never look at my camera on the Echo Show I just removed the Wyze skill and everything went back to the way it was. Since Alexa skills automatically update when a new version is available, it is conceivable that things like this could happen out of the blue one day and you'd have no idea what happened. It would be difficult to troubleshoot and determine that a skill update caused certain words or names not to work as they did previously.
Renegade, you mentioned that your device was called "stove." Do you have any skills that potentially could control some kitchen device? In the Alexa app, you can check the date when certain skills were updated. If you can narrow down when "stove" became a reserved name and a skill that was updated around the same time, that might help you find out what caused it.