Your caching hit rate looks healthy based on the settings you're using, the 'top missed urls' having minimal reporting misses, and the debug showing subsequent calls will be cache hits. Seeing a fluctuation between days is pretty normal, especially if you published new content.
Anything above 60% is really good caching, and the fact that there are days when 8/10 visits are cached is a sign that things are working properly.
We're not sure there's anything further to troubleshoot in this case, which is a good thing! 🙂