Thanks for the explanation and example, @CondorWonder.
I used Studio Code Server to search all files for "Automation: Turn Off" and "automation.turn_off" and "automation" - there were 100s (1000s?) of results. I scanned through them and didn't see anything that looks like it was enabling these automations. And that's the only record in my logbook around these automations being disabled.
So now I've renamed some of my automations and re-disabled them. In a few days they'll either become enabled or I'll search my logs for errors including their previous names.