How do I calibrate my auto tension belt?
I suspect the tensioner is working correctly, but the sprocket is starting to wear and is not holding the belt teeth properly.

You say that when the belt was slipping previously, it wore the sprocket away. I would not expect a reinforced rubber belt to severely damage a metal sprocket so presumably it is of a softer material such as aluminum or a composite plastic that is subject to wear even when the belt is not slipping.

Inspect the sprocket and see if there are wear marks visible on the teeth.

It’s also possible is that the belt itself is worn as well.